doc: add tip for NODE_MODULE

Author: theanarkh

doc/api/addons.md

@@ -107,6 +107,14 @@ When building addons with `node-gyp`, using the macro `NODE_GYP_MODULE_NAME` as
 the first parameter of `NODE_MODULE()` will ensure that the name of the final
 binary will be passed to `NODE_MODULE()`.
 
+If you define addon with `NODE_MODULE`, The usage is as follows.
+
+1. If you load the addon in main thread first, you can not load the addon
+   in worker.
+2. If you load the addon in worker first, you can not load the addon in
+   main thread, and you can only load the addon in another worker after the
+   worker which have loaded the addon exsits.
+
 ### Context-aware addons
 
 There are environments in which Node.js addons may need to be loaded multiple