Add details to docs on how to extend PR tests

.github/PULL_REQUEST_TEMPLATE.md

@@ -19,6 +19,7 @@ Remove this section if not relevant
 ### Commits signed with GPG?
 Yes/No
 
-Please review [Salt's Contributing Guide](https://docs.saltproject.io/en/master/topics/development/contributing.html) for best practices.
+Please review [Salt's Contributing Guide](https://docs.saltproject.io/en/master/topics/development/contributing.html) for best practices, including the
+[PR Guidelines](https://docs.saltproject.io/en/master/topics/development/pull_requests.html).
 
 See GitHub's [page on GPG signing](https://help.github.com/articles/signing-commits-using-gpg/) for more information about signing commits with GPG.

doc/topics/development/pull_requests.rst

@@ -185,3 +185,43 @@ PR's that do not require tests include:
   * fixing tests
   * pylint
   * changes outside of the salt directory
+
+Pull Request CI/CD test suite
+=============================
+
+By default, PRs run a limited subset of the test suite against the following
+operating systems:
+
+* Linux:
+    - Latest ``Rocky Linux x86_64``
+    - Latest ``Amazon Linux aarch64``
+    - Latest ``Ubuntu LTS arm64``
+    - Latest ``Arch Linux x86_64``
+* Latest ``Windows Server x86_64``
+* Latest ``MacOS arm64``
+
+Optional OS additions
+---------------------
+
+There are times where a PR is specifically addressing a target OS, or a core component of
+Salt is being updated that needs to be tested against all support operating systems. This
+is often required to fix ``nightly`` builds, or introduce a new operating system into CI/CD.
+
+Labels can be applied to a PR, via those who have the appropriate permissions, using the
+``test:os:<os-name><os-arch>`` format.
+
+* Example: ``test:os:debian-11-arm64`` would also ensure the Debian 11 arm64 OS is included.
+
+Optionally, ``test:os:all`` can be used as a way to target all operating systems
+that nightlies, staging, release target without having to add them all individually.
+
+Optional test additions
+-----------------------
+
+If wanting to also increase the scope of tests themselves, not just the scope of operating
+systems, then additional labels can be used such as:
+
+* ``test:pkg``: Run all package-related tests that are otherwise not included by default
+  on the currently selected operating systems.
+* ``test:full``: Run all tests in the Salt test suite that can be ran on the currently
+  selected operating systems.