Documentation (CONTRIBUTING): How to use Pylint, flake8 and tox

[avara1986]

Update CONTRIBUTING.md with information about linters and tools and ways of use these:

• Pylint: link to official documentation, how can i execute the command, benefits of pylintrc
• Flake8: link to official documentation, how can i execute the command, benefits of define params in setup.cfg
• Tox: link to official documentation
• Mypy: link to official documentation, benefits of define params in setup.cfg (PR open to add this tool)
• setup.cfg: what's mean this file

Moved from python-microservices/pyms#168