Add google.auth.jwt (#7)

diff --git a/docs/reference/google.auth.rst b/docs/reference/google.auth.rst
index 4c39cb9..57a16b4 100644
--- a/docs/reference/google.auth.rst
+++ b/docs/reference/google.auth.rst
@@ -12,4 +12,5 @@
 .. toctree::
 
    google.auth.crypt
+   google.auth.jwt