add pre-commit to CONTRIBUTING.txt

CONTRIBUTING.rst

@@ -163,6 +163,7 @@ Short version
 ~~~~~~~~~~~~~
 
 #. Fork the repository;
+#. enable and install pre-commit https://pre-commit.com/ to ensure styleguides and codechecks are followed
 #. Target ``master`` for bugfixes and doc changes;
 #. Target ``features`` for new features or functionality changes.
 #. Follow **PEP-8**. There's a ``tox`` command to help fixing it: ``tox -e fix-lint``.
@@ -216,6 +217,16 @@ Here is a simple overview, with pytest-specific bits:
    If you need some help with Git, follow this quick start
    guide: https://git.wiki.kernel.org/index.php/QuickStart
 
+#. install pre-commit and install its hook on the pytest repo
+
+    https://pre-commit.com/ is a framework for managing and maintaining multi-language pre-commit hooks
+    pytest uses pre-commit to ensure code-style and code formatting is the same
+
+    $ pip install --user pre-commit
+    $ pre-commit install
+
+    Afterwards pre-commit will run whenever you commit.
+
 #. Install tox
 
    Tox is used to run all the tests and will automatically setup virtualenvs