Update the docs and CI schema for the new syntax of `rules: changes`

Summary

With rules: changes being updated in #293645 (closed), it is important that our documentation reflects these changes so users are informed of that.

Proposal

As a follow-up to #293645 (closed), we need to update the docs with the new syntax so that it reflects how rules: changes should be used.

Implementation Table

Group Issue Link
backend Backend: rules:changes / only:changes and new branches
documentation 👈 You are here

Links/References

Edited by Mark Nuzzo