Fix 404 link in Diviner to "Configuring File Storage" article

Summary: Fix a broken link in documentation.

Test Plan:

1. Go to https://we.phorge.it/book/dev/class/PhabricatorFileStorageEngine/
2. Click link "For more information, see File Storage Technical Documentation."
3. Get a 404 via https://we.phorge.it/diviner/find/?name=File_Storage_Technical_Documentation&type=article&jump=1 beforehand; get an article via https://we.phorge.it/diviner/find/?name=Configuring_File_Storage&type=article&jump=1 afterhand.

Reviewers: O1 Blessed Committers, valerio.bozzolan

Reviewed By: O1 Blessed Committers, valerio.bozzolan

Subscribers: tobiaswiese, valerio.bozzolan, Matthew, Cigaryno

Differential Revision: https://we.phorge.it/D25762