Add google.auth.crypt (#6)

diff --git a/docs/reference/google.auth.rst b/docs/reference/google.auth.rst
index 0533449..4c39cb9 100644
--- a/docs/reference/google.auth.rst
+++ b/docs/reference/google.auth.rst
@@ -6,3 +6,10 @@
     :undoc-members:
     :show-inheritance:
 
+Submodules
+----------
+
+.. toctree::
+
+   google.auth.crypt
+