R1:4b3dcd550075

Add some documentation about how to set paths with owners.edit

Summary:
Ref T9964.

- New mechanism for rich documentation on unusual/complicated edits.
- Add some docs to `paths.set` since it's not self-evident what you're supposed to pass in.

Test Plan: {F1027177}

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T9964

Differential Revision: https://secure.phabricator.com/D14791