docs: clarify the idea of best practice of installing in srv

This was introduced in 03bbd33bc084 as it seems like the best location based on
Filesystem Hierarchy Standard.

docs/installation.rst

@@ -84,6 +84,10 b' An additional benefit of virtualenv is t'
   If necessary, create the top directory for the virtualenv (like
   ``/srv/kallithea/venv``) as root and assign ownership to the user.
 
+  Make a parent folder for the virtualenv (and perhaps also Kallithea
+  configuration and data files) such as ``/srv/kallithea``. Create the
+  directory as root if necessary and grant ownership to the ``kallithea`` user.
+
 - Create a new virtual environment, for example in ``/srv/kallithea/venv``,
   specifying the right Python binary::
 

docs/overview.rst

@@ -74,6 +74,11 b' Kallithea can be installed in many diffe'
   This will have to be writable by the running Kallithea service. The path to
   this location will be configured in the database.
 
+For production setups, one recommendation is to use ``/srv/kallithea`` for the
+``.ini`` and ``data``, place the virtualenv in ``venv``, and use a Kallithea
+clone in ``kallithea``. Create a ``kallithea`` user, let it own
+``/srv/kallithea``, and run as that user when installing.
+
 For simple setups, it is fine to just use something like a ``kallithea`` user
 with home in ``/home/kallithea`` and place everything there.