Disallow webcrawlers to index Diffusion commits
Summary:
Phorge already sets `Disallow: /diffusion/` and `Disallow: /source/`.
Thus consequently also disallow accessing specific commits via `/r*`.
See https://secure.phabricator.com/T4610 for previous discussions.
Closes T15670
Test Plan:
Go to `/robots.txt` in the web browser.
Cross fingers that more webcrawlers abide by RFC 9309.
Reviewers: O1 Blessed Committers, speck
Reviewed By: O1 Blessed Committers, speck
Subscribers: tobiaswiese, valerio.bozzolan, Matthew, Cigaryno
Maniphest Tasks: T15670
Differential Revision: https://we.phorge.it/D25474