Add pull by digest example to the dependency proxy

doc/user/packages/dependency_proxy/index.md

@@ -94,9 +94,11 @@ Runners log in to the Dependency Proxy automatically. To pull through
 the Dependency Proxy, use the `CI_DEPENDENCY_PROXY_GROUP_IMAGE_PREFIX`
 [predefined CI/CD variable](../../../ci/variables/predefined_variables.md):
 
+Example pulling the latest alpine image:
+
 ```yaml
 # .gitlab-ci.yml
-image: ${CI_DEPENDENCY_PROXY_GROUP_IMAGE_PREFIX}/node:latest
+image: ${CI_DEPENDENCY_PROXY_GROUP_IMAGE_PREFIX}/alpine:latest
 ```
 
 There are other additional predefined CI/CD variables you can also use:
@@ -124,13 +126,20 @@ To store a Docker image in Dependency Proxy storage:
 1. Go to your group's **Packages & Registries > Dependency Proxy**.
 1. Copy the **Dependency Proxy URL**.
 1. Use one of these commands. In these examples, the image is `alpine:latest`.
+1. You can also pull images by digest to specify exactly which version of an image to pull.
 
-   - Add the URL to your [`.gitlab-ci.yml`](../../../ci/yaml/README.md#image) file:
+   - Pull an image by tag by adding the image to your [`.gitlab-ci.yml`](../../../ci/yaml/README.md#image) file:
 
      ```shell
      image: gitlab.example.com/groupname/dependency_proxy/containers/alpine:latest
      ```
 
+   - Pull an image by digest by adding the image to your [`.gitlab-ci.yml`](../../../ci/yaml/README.md#image) file:
+
+     ```shell
+     image: ${CI_DEPENDENCY_PROXY_GROUP_IMAGE_PREFIX}/alpine@sha256:c9375e662992791e3f39e919b26f510e5254b42792519c180aad254e6b38f4dc
+     ```
+
    - Manually pull the Docker image:
 
      ```shell