help commands

def cmd_help(self, args):
        '''help commands'''
        if len(args) < 1:
            self.print_usage()
            return

        if args[0] == "about":
            print(self.about_string())
        elif args[0] == "site":
            print("See http://ardupilot.github.io/MAVProxy/ for documentation")
        else:
            self.print_usage()