Update mg_start_thread.md

docs/c-api/util.h/mg_start_thread.md

@@ -6,8 +6,8 @@ signature: |
   void *mg_start_thread(void *(*thread_func);
 ---
 
-Start a new detached thread.
-Arguments and semantic is the same as pthead's `pthread_create()`.
+Starts a new detached thread.
+Arguments and semantics are the same as pthead's `pthread_create()`.
 `thread_func` is a thread function, `thread_func_param` is a parameter
 that is passed to the thread function.