Updated Interfaces (markdown)

Interfaces.md

@@ -6,6 +6,8 @@ ggs_vm_runner:define(GameVM, SourceCode) -> ok
 ggs_vm_runner:user_command(GameVM, User, Command, Args) -> ok
 </pre>
 
+Only `start_link()` has a return value, the other two always return `ok`.
+
 ## ggs_server
 <pre>
 handle_cast(stop, State) -> {stop, normal, State}