i18n: help: mark strings for translation

This patch also marks most common commands' synopsis for translation
so that "git help" gives a friendly listing.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

generate-cmdlist.sh

@@ -16,7 +16,7 @@ do
      /^NAME/,/git-'"$cmd"'/H
      ${
 	    x
-	    s/.*git-'"$cmd"' - \(.*\)/  {"'"$cmd"'", "\1"},/
+	    s/.*git-'"$cmd"' - \(.*\)/  {"'"$cmd"'", N_("\1")},/
 	    p
      }' "Documentation/git-$cmd.txt"
 done