Updated mediawiki/extensions
Project: mediawiki/extensions/MobileFrontend  89f8331432e4582efd113b412ee30f5cdc3bef6d

Document the commands in the Makefile

Also introduce a help command that extracts and outputs the
documentation from the Makefile.

Bug: 71892
Change-Id: I1aa1f4a83650df3bc3427215004dda09e5dff1b5