Document running tests against Graph API

Author: dan-silver

README.md

@@ -306,7 +306,9 @@ These steps are not required to use this library.
 
 ```npm pack``` bundles the npm module.
 
-```npm test``` runs tests.
+```npm test``` runs tests of the core library (URL parsing, mock responses, etc)
+
+```npm run test:types``` to run tests against the Graph API for users, groups, Excel, OneNote, etc.
 
 To build only browser version:
 ```