Docs: document "force https" for Pages

doc/user/project/pages/getting_started_part_three.md

 ---
-last_updated: 2019-06-04
+last_updated: 2019-06-25
 type: concepts, reference, howto
 ---
 
@@ -138,9 +138,9 @@ verify your domain's ownership with a TXT record:
 > - **Do not** add any special chars after the default Pages
   domain. E.g., **do not** point your `subdomain.domain.com` to
   `namespace.gitlab.io.` or `namespace.gitlab.io/`.
-> - GitLab Pages IP on GitLab.com [was changed](https://about.gitlab.com/2017/03/06/we-are-changing-the-ip-of-gitlab-pages-on-gitlab-com/) in 2017
+> - GitLab Pages IP on GitLab.com [was changed](https://about.gitlab.com/2017/03/06/we-are-changing-the-ip-of-gitlab-pages-on-gitlab-com/) in 2017.
 > - GitLab Pages IP on GitLab.com [has been changed](https://about.gitlab.com/2018/07/19/gcp-move-update/#gitlab-pages-and-custom-domains)
-  from `52.167.214.135` to `35.185.44.232` in 2018
+  from `52.167.214.135` to `35.185.44.232` in 2018.
 
 ### Add your custom domain to GitLab Pages settings
 
@@ -199,7 +199,7 @@ Certificates are NOT required to add to your custom
 highly recommendable.
 
 Let's start with an introduction to the importance of HTTPS.
-Alternatively, jump ahead to [adding certificates to your project](#adding-certificates-to-your-project).
+Alternatively, jump ahead to [adding certificates to your project](#adding-certificates-to-pages).
 
 ### Why should I care about HTTPS?
 
@@ -255,12 +255,12 @@ which also offers a [free CDN service](https://blog.cloudflare.com/cloudflares-f
 Their certs are valid up to 15 years. See the tutorial on
 [how to add a CloudFlare Certificate to your GitLab Pages website](https://about.gitlab.com/2017/02/07/setting-up-gitlab-pages-with-cloudflare-certificates/).
 
-### Adding certificates to your project
+### Adding certificates to Pages
 
 Regardless the CA you choose, the steps to add your certificate to
 your Pages project are the same.
 
-### What do you need
+#### Requirements
 
 1. A PEM certificate
 1. An intermediate certificate
@@ -270,7 +270,7 @@ your Pages project are the same.
 
 These fields are found under your **Project**'s **Settings** > **Pages** > **New Domain**.
 
-### What's what?
+#### Certificate types
 
 - A PEM certificate is the certificate generated by the CA,
   which needs to be added to the field **Certificate (PEM)**.
@@ -283,21 +283,32 @@ These fields are found under your **Project**'s **Settings** > **Pages** > **New
 - A private key is an encrypted key which validates
   your PEM against your domain.
 
-### Now what?
+#### Add the certificate to your project
 
-Now that you hopefully understand why you need all
-of this, it's simple:
+Once you've met the requirements:
 
-- Your PEM certificate needs to be added to the first field
+- Your PEM certificate needs to be added to the first field.
 - If your certificate is missing its intermediate, copy
   and paste the root certificate (usually available from your CA website)
   and paste it in the [same field as your PEM certificate](https://about.gitlab.com/2017/02/07/setting-up-gitlab-pages-with-cloudflare-certificates/),
   just jumping a line between them.
-- Copy your private key and paste it in the last field
+- Copy your private key and paste it in the last field.
 
->**Note:**
+NOTE: **Note:**
 **Do not** open certificates or encryption keys in
 regular text editors. Always use code editors (such as
 Sublime Text, Atom, Dreamweaver, Brackets, etc).
 
-_Read on about [Creating and Tweaking GitLab CI/CD for GitLab Pages](getting_started_part_four.md)_
+## Force HTTPS for GitLab Pages websites
+
+> [Introduced](https://gitlab.com/gitlab-org/gitlab-ce/issues/28857) in GitLab 10.7.
+
+To make your website's visitors even more secure, you can choose to
+force HTTPS for GitLab Pages. By doing so, all attempts to visit your
+website via HTTP will be automatically redirected to HTTPS via 301.
+
+It works with both GitLab's default domain and with your custom
+domain (as long as you've set a valid certificate for it).
+
+To enable this setting, navigate to your project's **Settings > Pages**
+and tick the checkbox **Force HTTPS (requires valid certificates)**.