Add guidance about creating and including snippets in docs for contributors.

[snneji]

Context

To prevent duplication in docs we want to implement a snippets feature that meets our needs.

Tasks

1. After Implement new snippet plugin including offset functionality #4556 is closed, document how to use the snippets plugin in the docs contributor guide.

[github-actions]

This issue is stale because it has been open for 90 days with no
activity. It will automatically close after 30 more days of
inactivity. Reopen the issue with /reopen. Mark the issue as
fresh by adding the comment /remove-lifecycle stale.

[snneji]

/lifecycle frozen