Add description for nthread_has_500ms_passed (#2141)

Source/nthread.cpp

@@ -222,6 +222,12 @@ void nthread_ignore_mutex(BOOL bStart)
 	}
 }
 
+/**
+ * @brief Checks if it's time for the logic to advance
+ * @param unused
+ * @return True if the engine should tick
+
+ */
 BOOL nthread_has_500ms_passed(BOOL unused)
 {
 	DWORD currentTickCount;