docs: Remove extra 'B' from PHP config value

Summary:
Turns out that if you specify 32MB PHP interprets that as 32 bytes,
which is not what you want.

Test Plan:
Checked that file uploads start working on my Phorge instance after
removing the trailing 'B'.

Reviewers: O1 Blessed Committers, avivey

Reviewed By: O1 Blessed Committers, avivey

Subscribers: tobiaswiese, valerio.bozzolan, Matthew, Cigaryno

Differential Revision: https://we.phorge.it/D25851