add details of the endpoint uri for "int.nugettest.org" (NuGet#1313)

* add details of the API Endpoint for "int.nugettest.org"

Author: Rob Relyea

docs/faqs/NuGet-FAQ.md

@@ -161,7 +161,7 @@ NuGet recommends all packages to be signed. A design principle of package signin
 
 Note that dependencies listed for your package are generated automatically from the package itself and cannot be edited.
 
-In addition, uploading packages to [int.nugettest.org](https://int.nugettest.org) is a great way to test and validate your package without making a package available in the public gallery.
+In addition, uploading packages to [int.nugettest.org](https://int.nugettest.org) is a great way to test and validate your package without making a package available in the public gallery. API Endpoint: https://apiint.nugettest.org/v3/index.json
 
 **Is it possible to reserve names for packages that will be published in future?**