readme: add google drive link (#5)

Author: FFY00

README.rst

@@ -6,3 +6,11 @@ interact with some Logitech devices.
 
 Protocol index:
   - `HID++ 2.0 <hidpp20>`_
+
+The final goal of this repository is to expose the documentation in a
+uniform format. While we achieve this, some documentation is
+available albeit in various shapes. Hoping that they will be
+useful 'as is' they can be obtained from this `Google Drive
+folder`_.
+
+.. _Google Drive folder: https://drive.google.com/drive/u/0/folders/0BxbRzx7vEV7eWmgwazJ3NUFfQ28