Option to add CONTRIBUTING.md to the project

[vrom911]

I think that ability to have CONTRIBUTING.md in open-source projects is quite useful. There is huge amount of different variations of it and it's actually a matter of taste, but few things can be done about this feature.

• Simple file can be generated with neutral information that is applicable to any Haskell project (like I have here, but better).
• or you can specify your repository (ex. : hs-init) or any other user's repository (ex. : user/repo) and the copy of the CONTRIBUTING.md file from there will be added to the project.