Added code to output the top level command options if docker-compose help with no command options provided

Signed-off-by: Tony Witherspoon <tony.witherspoon@gmail.com>

compose/cli/main.py

@@ -355,10 +355,14 @@ class TopLevelCommand(object):
         """
         Get help on a command.
 
-        Usage: help COMMAND
+        Usage: help [COMMAND]
         """
-        handler = get_handler(cls, options['COMMAND'])
-        raise SystemExit(getdoc(handler))
+        if options['COMMAND']:
+            subject = get_handler(cls, options['COMMAND'])
+        else:
+            subject = cls
+
+        print(getdoc(subject))
 
     def kill(self, options):
         """