mwdocgen.php going to require a LocalSettings.php

I have overhauled the old mwdocgen.php script to make it depends on
the Maintenance class: https://gerrit.wikimedia.org/r/#/c/64866/

A side effect pointed by PleaseStand, is that the wrapper now requires a
LocalSettings.php file.  Using touch will create an empty file if it not
there.

bug: 34436
Change-Id: Ia4ab471f810b352acdc1453a55773a0f99727a53