[doc/book] add RQL use cases with search/card/python/javascript
Related to https://www.cubicweb.org/ticket/3899077
.. _RQLChapter:
Relation Query Language (RQL)
=============================
This chapter describes the Relation Query Language syntax and its implementation in CubicWeb.
.. toctree::
:maxdepth: 2
intro
language
debugging
usecases
implementation