doc: update blurb explaining NODE_ADDON_API

Fixes: nodejs/node-addon-api#249
PR-URL: nodejs/node-addon-api#251
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>

doc/node-gyp.md

@@ -58,10 +58,12 @@ Napi::Object Init(Napi::Env env, Napi::Object exports) {
 /**
 * This code defines the entry-point for the Node addon, it tells Node where to go
 * once the library has been loaded into active memory. The first argument must
-* match the "target" in our *binding.gyp*. The second argument points to the
-* function to invoke.
+* match the "target" in our *binding.gyp*. Using NODE_GYP_MODULE_NAME ensures
+* that the argument will be correct, as long as the module is built with
+* node-gyp (which is the usual way of building modules). The second argument
+* points to the function to invoke. The function must not be namespaced.
 */
-NODE_API_MODULE(myModule, Init)
+NODE_API_MODULE(NODE_GYP_MODULE_NAME, Init)
 ```
 
 ## **node-gyp** reference