Add basic structure for plain tutorial

- `tutorial.rst` is now `tutorial-relay.rst`
- Added `tutorial-plain.rst`

Author: Radoslav Georgiev

docs/index.rst

@@ -6,7 +6,8 @@ Contents:
 .. toctree::
    :maxdepth: 0
 
-   tutorial
+   tutorial-plain
+   tutorial-relay
    filtering
    authorization
    debug