more detailed instructions for using github container registry (#5099)

* more detailed instructions for using github container registry

* Update instructions for cross OS compatibility

Author: PhilBastian

docs/testing.md

@@ -43,6 +43,15 @@ Container images generated for all builds are pushed to the [GitHub container re
 Containers built by a PR and stored on GitHub Container Registry can be tested locally:
 
 1. [Authenticate to the GitHub Container Registry using a personal access token](https://docs.github.com/en/packages/working-with-a-github-packages-registry/working-with-the-container-registry#authenticating-with-a-personal-access-token-classic).
+    - Create a [classic token](https://github.com/settings/tokens). Select the scope for `read:packages`
+    - Copy the newly created token text.
+    - Run the following command in a terminal:
+       ```shell
+       docker login ghcr.io
+       ```
+      you will be prompted for a username (your particular.net email) and a password (the token)
+    - ensure that you get a successful login message.
+    - Use `docker logout ghcr.io` once the following steps are complete and consider removing the token from github if its no longer needed
 2. In the terminal, navigate to `[/docs/test-ghcr-tag`](/docs/test/ghcr-tag).
 3. Edit the [`.env` file](/docs/test-ghcr-tag/.env) to specify the PR-based tag (in the form `pr-####`) to test.
 4. Run `docker compose up -d`.