Improve the Review Apps documentation a bit

Signed-off-by: Rémy Coutable <remy@rymai.me>

doc/development/testing_guide/review_apps.md

-# Review apps
+# Review Apps
 
 Review Apps are automatically deployed by each pipeline, both in
 [CE](https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/22010) and
@@ -9,67 +9,74 @@ Review Apps are automatically deployed by each pipeline, both in
 1. On every [pipeline][gitlab-pipeline] during the `test` stage, the
   [`review` job][review-job] is automatically started.
 1. The `review` job [triggers a pipeline][cng-pipeline] in the
-  [`CNG-mirror`][cng-mirror] [^1] project
-1. The `CNG-mirror` pipeline creates the Docker images of each component (e.g. `gitlab-rails-ee`,
-  `gitlab-shell`, `gitaly` etc.) based on the commit from the
+  [`CNG-mirror`][cng-mirror] project.
+    - We use the `CNG-mirror` project so that the `CNG`, (**C**loud **N**ative
+      **G**itLab), project's registry is not overloaded with a lot of transient
+      Docker images.
+1. The `CNG-mirror` pipeline creates the Docker images of each component (e.g.
+  `gitlab-rails-ee`, `gitlab-shell`, `gitaly` etc.) based on the commit from the
   [GitLab pipeline][gitlab-pipeline] and store them in its
-  [registry][cng-mirror-registry]
-1. Once all images are built, the review app is deployed using
-  [the official GitLab Helm chart][helm-chart] [^2] to the
+  [registry][cng-mirror-registry].
+1. Once all images are built, the Review App is deployed using
+  [the official GitLab Helm chart][helm-chart] to the
   [`review-apps-ee` Kubernetes cluster on GCP][review-apps-ee]
-  - The actual scripts used to deploy the review app can be found at
+    - The actual scripts used to deploy the Review App can be found at
       [`scripts/review_apps/review-apps.sh`][review-apps.sh]
     - These scripts are basically
       [our official Auto DevOps scripts][Auto-DevOps.gitlab-ci.yml] where the
       default CNG images are overriden with the images built and stored in the
-    [`CNG-mirror` project's registry][cng-mirror-registry]
-1. Once the `review` job succeeds, you should be able to use your review app
+      [`CNG-mirror` project's registry][cng-mirror-registry].
+    - Since we're using [the official GitLab Helm chart][helm-chart], this means
+      you get a dedicated environment for your branch that's very close to what it
+      would look in production.
+1. Once the `review` job succeeds, you should be able to use your Review App
   thanks to the direct link to it from the MR widget. The default username is
   `root` and its password can be found in the 1Password secure note named
-  **gitlab-{ce,ee} review app's root password**.
+  **gitlab-{ce,ee} Review App's root password** (note that there's currently
+  [a bug where the default password seems to be overriden][password-bug]).
 
 **Additional notes:**
 
-- The Kubernetes cluster is connected to the `gitlab-ee` project using [GitLab's
-  Kubernetes integration][gitlab-k8s-integration]. This basically allows to have
-  a link to the review app directly from the merge request widget.
-- The manual `stop_review` in the `post-cleanup` stage can be used to stop a
-  review app manually, and is also started by GitLab once a branch is deleted
-- [TBD] Review apps are cleaned up regularly using a pipeline schedule that runs
-  the [`scripts/review_apps/automated_cleanup.rb`][automated_cleanup.rb] script
-- If you're unable to log in using the `root` username and password, the 
-  deployment may have failed. Stop the Review App via the `stop_review` 
+- The Kubernetes cluster is connected to the `gitlab-{ce,ee}` projects using
+  [GitLab's Kubernetes integration][gitlab-k8s-integration]. This basically
+  allows to have a link to the Review App directly from the merge request widget.
+- The manual `stop_review` in the `test` stage can be used to stop a Review App
+  manually, and is also started by GitLab once a branch is deleted.
+- Review Apps are cleaned up regularly using a pipeline schedule that runs
+  the [`scripts/review_apps/automated_cleanup.rb`][automated_cleanup.rb] script.
+- If the Review App deployment fails, you can simply retry it (there's no need
+  to run the `stop_review` job first).
+- If you're unable to log in using the `root` username and password, you may
+  encounter [this bug][password-bug]. Stop the Review App via the `stop_review`
   manual job and then retry the `review` job to redeploy the Review App.
 
-[^1]: We use the `CNG-mirror` project so that the `CNG`, (**C**loud **N**ative **G**itLab), project's registry is
-  not overloaded with a lot of transient Docker images.
-[^2]: Since we're using [the official GitLab Helm chart][helm-chart], this means
-  you get the a dedicated environment for your branch that's very close to what it
-  would look in production
-
 ## Frequently Asked Questions
 
-**Will it be too much to trigger CNG image builds on every test run? This could create thousands of unused docker images.**
+**Isn't it too much to trigger CNG image builds on every test run? This creates
+thousands of unused Docker images.**
 
-  > We have to start somewhere and improve later. If we see this getting out of hand, we will revisit.
+  > We have to start somewhere and improve later. Also, we're using the
+  CNG-mirror project to store these Docker images so that we can just wipe out
+  the registry at some point, and use a new fresh, empty one.
 
-**How big is the Kubernetes cluster?**
+**How big are the Kubernetes clusters (`review-apps-ce` and `review-apps-ee`)?**
 
-  > The cluster is currently setup with a single pool of preemptible
-    nodes, with a minimum of 1 node and a maximum of 30 nodes.
+  > The clusters are currently set up with a single pool of preemptible nodes,
+  with a minimum of 1 node and a maximum of 100 nodes.
 
 **What are the machine running on the cluster?**
 
   > We're currently using `n1-standard-4` (4 vCPUs, 15 GB memory) machines.
 
-**How do we secure this from abuse? Apps are open to the world so we need to find a way to limit it to only us.**
+**How do we secure this from abuse? Apps are open to the world so we need to
+find a way to limit it to only us.**
 
-  > This won't work for forks. We will add a root password to 1password shared vault.
+  > This isn't enabled for forks.
 
-[gitlab-pipeline]: https://gitlab.com/gitlab-org/gitlab-ee/pipelines/29302122
-[review-job]: https://gitlab.com/gitlab-org/gitlab-ee/-/jobs/94294136
+[gitlab-pipeline]: https://gitlab.com/gitlab-org/gitlab-ce/pipelines/35850709
+[review-job]: https://gitlab.com/gitlab-org/gitlab-ce/-/jobs/118076368
 [cng-mirror]: https://gitlab.com/gitlab-org/build/CNG-mirror
-[cng-pipeline]: https://gitlab.com/gitlab-org/build/CNG-mirror/pipelines/29307727
+[cng-pipeline]: https://gitlab.com/gitlab-org/build/CNG-mirror/pipelines/35883435
 [cng-mirror-registry]: https://gitlab.com/gitlab-org/build/CNG-mirror/container_registry
 [helm-chart]: https://gitlab.com/charts/gitlab/
 [review-apps-ee]: https://console.cloud.google.com/kubernetes/clusters/details/us-central1-b/review-apps-ee?project=gitlab-review-apps
@@ -77,6 +84,7 @@ Review Apps are automatically deployed by each pipeline, both in
 [automated_cleanup.rb]: https://gitlab.com/gitlab-org/gitlab-ee/blob/master/scripts/review_apps/automated_cleanup.rb
 [Auto-DevOps.gitlab-ci.yml]: https://gitlab.com/gitlab-org/gitlab-ce/blob/master/lib/gitlab/ci/templates/Auto-DevOps.gitlab-ci.yml
 [gitlab-k8s-integration]: https://docs.gitlab.com/ee/user/project/clusters/index.html
+[password-bug]: https://gitlab.com/gitlab-org/gitlab-ce/issues/53621
 
 ---