[doc] update a bit the documentation
Also convert the README in rst (so it can be properly displayed on
cubicweb.org).
.. _login_module:
:mod:`pyramid_cubicweb.login`
-----------------------------
.. automodule:: pyramid_cubicweb.login
.. autofunction:: includeme
Views
-----
.. autofunction:: login_form
.. autofunction:: login_password_login
.. autofunction:: login_already_loggedin