git: Autoload helper functions for 'run-help'

Now that, prezto is configured to lookup more specific 'run-help'
function, autoload the known one for git.

modules/git/init.zsh

@@ -13,5 +13,8 @@ fi
 # Load dependencies.
 pmodload 'helper'
 
+# Load 'run-help' function.
+autoload -Uz run-help-git
+
 # Source module files.
 source "${0:h}/alias.zsh"