Add oauth2 credentials (#24)

diff --git a/docs/reference/google.oauth2.credentials.rst b/docs/reference/google.oauth2.credentials.rst
new file mode 100644
index 0000000..ca978d1
--- /dev/null
+++ b/docs/reference/google.oauth2.credentials.rst
@@ -0,0 +1,7 @@
+google.oauth2.credentials module
+================================
+
+.. automodule:: google.oauth2.credentials
+    :members:
+    :inherited-members:
+    :show-inheritance: