readme: Use git.wikimedia.org instead of gerrit
readme: Use git.wikimedia.org instead of gerrit

Also drop --depth since shallow copies are known to have issues when
kept alive for a long time and random shit happens (see #1).
Krinkle/mw-tool-snapshots,paladox/mw-tool-snapshots,Krinkle/mw-tool-snapshots,paladox/mw-tool-snapshots