Add http.client transport (#10)

diff --git a/docs/reference/google.auth.rst b/docs/reference/google.auth.rst
index 57a16b4..0f147e9 100644
--- a/docs/reference/google.auth.rst
+++ b/docs/reference/google.auth.rst
@@ -6,11 +6,19 @@
     :undoc-members:
     :show-inheritance:
 
+Subpackages
+-----------
+
+.. toctree::
+
+    google.auth.transport
+
 Submodules
 ----------
 
 .. toctree::
 
    google.auth.crypt
+   google.auth.exceptions
    google.auth.jwt