Add descriptions to module commands

Each module command has to describe what it does. This should make module
commands self-documenting to some degree.

server/modules/routing/avrorouter/avro.c

@@ -148,7 +148,9 @@ MXS_MODULE* MXS_CREATE_MODULE()
         { MODULECMD_ARG_SERVICE | MODULECMD_ARG_NAME_MATCHES_DOMAIN, "The avrorouter service" },
         { MODULECMD_ARG_STRING, "Action, whether to 'start' or 'stop' the conversion process" }
     };
-    modulecmd_register_command(MXS_MODULE_NAME, "convert", MODULECMD_TYPE_ACTIVE, avro_handle_convert, 2, args);
+    modulecmd_register_command(MXS_MODULE_NAME, "convert", MODULECMD_TYPE_ACTIVE,
+                               avro_handle_convert, 2, args,
+                               "Start or stop the binlog to avro conversion process");
 
     static MXS_ROUTER_OBJECT MyObject =
     {