Contribute to CONTRIBUTING document

[LuckyPigeon]

I want to contribute to CONTRIBUTING document about after making changing, last time I couldn't use py.test but use python setup.py install did work, so I want to write that on the document

[PrabhanshuAttri]

Please create a PR. If it's good enough, I will merge it.

[LuckyPigeon]

Sorry for I didn't delete the env file, I have already make some changes and pull another request, sould I create another issue for removing the env file?

[PrabhanshuAttri]

Please comment on related issue/PR only.