git-remote-mediawiki: add a perlcritic rule in Makefile

Option "-2" launches perlcritic with level 2. Levels go from 5 (most pertinent)
to 1. Rules of level 1 are mostly a question of style, and are therefore
ignored.

Signed-off-by: Célestin Matte <celestin.matte@ensimag.fr>
Signed-off-by: Matthieu Moy <matthieu.moy@grenoble-inp.fr>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

contrib/mw-to-git/Makefile

@@ -15,3 +15,5 @@ all: build
 build install clean:
 	$(MAKE) -C $(GIT_ROOT_DIR) SCRIPT_PERL=$(SCRIPT_PERL_FULL) \
                 $@-perl-script
+perlcritic:
+	perlcritic -2 *.perl