It is hard to find and learn about RPC in Odoo, users hardly know about
JSON-RPC as the only place where we talk about it in deep down in the
*How to make a Module* tutorial.
In the commit, we isolated the tutorial about RPC in a dedicated file,
that file is better referenced thanks to cross-references in some others
places that are talking about RPC
Task: 2884559
X-original-commit: 83c2e6de0b
Part-of: odoo/documentation#2719
