Add downscoping to ouath2 credentials (#309)


diff --git a/docs/reference/google.auth.crypt.rst b/docs/reference/google.auth.crypt.rst
index 26b8b4a..a3e2b12 100644
--- a/docs/reference/google.auth.crypt.rst
+++ b/docs/reference/google.auth.crypt.rst
@@ -1,7 +1,16 @@
-google.auth.crypt module
-========================
+google.auth.crypt package
+=========================
 
 .. automodule:: google.auth.crypt
     :members:
     :inherited-members:
     :show-inheritance:
+
+Submodules
+----------
+
+.. toctree::
+
+   google.auth.crypt.base
+   google.auth.crypt.rsa
+