docs(readme): modify according to standard structure

docs/README.rst

-=================
+.. _readme:
+
 firewalld-formula
 =================
 
-Salt Stack Formula to set up and configure Firewalld, dynamically managed firewall with support for network/firewall zones to define the trust level of network connections or interfaces
+|img_travis| |img_sr|
+
+.. |img_travis| image:: https://travis-ci.com/saltstack-formulas/firewalld-formula.svg?branch=master
+   :alt: Travis CI Build Status
+   :scale: 100%
+   :target: https://travis-ci.com/saltstack-formulas/firewalld-formula
+.. |img_sr| image:: https://img.shields.io/badge/%20%20%F0%9F%93%A6%F0%9F%9A%80-semantic--release-e10079.svg
+   :alt: Semantic Release
+   :scale: 100%
+   :target: https://github.com/semantic-release/semantic-release
+
+A SaltStack Formula to set up and configure Firewalld, a dynamically managed firewall with support for network/firewall zones to define the trust level of network connections or interfaces.
+
+.. contents:: **Table of Contents**
+
+General notes
+-------------
 
-.. image:: https://travis-ci.org/saltstack-formulas/firewalld-formula.svg?branch=master
+See the full `SaltStack Formulas installation and usage instructions
+<https://docs.saltstack.com/en/latest/topics/development/conventions/formulas.html>`_.
 
-NOTICE BEFORE YOU USE
-=====================
+If you are interested in writing or contributing to formulas, please pay attention to the `Writing Formula Section
+<https://docs.saltstack.com/en/latest/topics/development/conventions/formulas.html#writing-formulas>`_.
 
-* This formula aims to follow the conventions and recommendations described at http://docs.saltstack.com/topics/conventions/formulas.html
+If you want to use this formula, please pay attention to the ``FORMULA`` file and/or ``git tag``,
+which contains the currently released version. This formula is versioned according to `Semantic Versioning <http://semver.org/>`_.
+
+See `Formula Versioning Section <https://docs.saltstack.com/en/latest/topics/development/conventions/formulas.html#versioning>`_ for more details.
+
+If you need (non-default) configuration, please pay attention to the ``pillar.example`` file and/or `Special notes`_ section.
+
+Contributing to this repo
+-------------------------
+
+**Commit message formatting is significant!!**
+
+Please see `How to contribute <https://github.com/saltstack-formulas/.github/blob/master/CONTRIBUTING.rst>`_ for more details.
+
+Special notes
+-------------
+
+None
 
 TODO
-====
+----
 
 * configure local pre-commit hooks (code syntax check based on file extension, check for ugly *utf-8 mac os white space*)
 
 Instructions
-============
+------------
 
 1. Add this repository as a `GitFS <http://docs.saltstack.com/topics/tutorials/gitfs.html>`_ backend in your Salt master config.
 
 
 3. Include this Formula within another Formula or simply define your needed states within the Salt top file (``/srv/salt/top.sls``).
 
-Available states
-================
-
-.. contents::
-    :local:
-
-``firewalld``
--------------
-Manage firewalld
-
 Additional resources
-====================
+--------------------
 
 None
 
 Formula Dependencies
-====================
+--------------------
 
 None
 
 Contributions
-=============
+-------------
 
 Contributions are always welcome. All development guidelines you have to know are
 
 * update README.rst doc
 
 Salt Compatibility
-==================
+------------------
 
 Tested with:
 
 * 2018.3.x (will probably work too with 2017.x.x)
 
 OS Compatibility
-================
+----------------
 
 Tested with:
 
 * CentOS 7
 * Debian 9
 * Ubuntu 18.04
+
+Available states
+----------------
+
+.. contents::
+   :local:
+
+``firewalld``
+^^^^^^^^^^^^^
+
+Manage firewalld
+
+Testing
+-------
+
+Linux testing is done with ``kitchen-salt``.
+
+Requirements
+^^^^^^^^^^^^
+
+* Ruby
+* Docker
+
+.. code-block:: bash
+
+   $ gem install bundler
+   $ bundle install
+   $ bin/kitchen test [platform]
+
+Where ``[platform]`` is the platform name defined in ``kitchen.yml``,
+e.g. ``debian-9-2019-2-py3``.
+
+``bin/kitchen converge``
+^^^^^^^^^^^^^^^^^^^^^^^^
+
+Creates the docker instance and runs the ``firewalld`` main state, ready for testing.
+
+``bin/kitchen verify``
+^^^^^^^^^^^^^^^^^^^^^^
+
+Runs the ``inspec`` tests on the actual instance.
+
+``bin/kitchen destroy``
+^^^^^^^^^^^^^^^^^^^^^^^
+
+Removes the docker instance.
+
+``bin/kitchen test``
+^^^^^^^^^^^^^^^^^^^^
+
+Runs all of the stages above in one go: i.e. ``destroy`` + ``converge`` + ``verify`` + ``destroy``.
+
+``bin/kitchen login``
+^^^^^^^^^^^^^^^^^^^^^
+
+Gives you SSH access to the instance for manual testing.