Refactor documentation: README, CONTRIBUTING and docs

[alexamici]

• [x] README is the landing page in GitHub and PyPI so it targets the final users (python developer). It shall:
  • [x] inspire and raise interest
  • [x] BIG AND FAT WARNING: all functions include shutil.rmtree and many other monsters.
  • [x] basic installation and usage instructions
  • [x] complete interesting usage example, e.g. distutils.util.strtobool
  • [x] give pointers to the project resources:
  • [x] how to get help / stackoverflow link
  • [x] issue tracker
  • [x] documentation
  • [x] parent website, http://nodev.io
  • [x] advertise credit to main contributors
  • [x] advertise license
• [ ] CONTRIBUTING is linked when opening a Pull Request on GitHub so it targets potential contributors, both experienced and newcomers. It shall:
  • [x] note the implicit acceptance of the LICENCE
  • [ ] give policies on use of resources:
  • [x] issue tracker
  • [x] pull requests
  • [ ] stackoverflow questions
  • [ ] code style guide and guidelines
  • [x] expected development quality assurance:
  • [x] pytest + tox + coverage
  • [x] discussion forum or mailing list or slack
• [x] full package documentation hosted on readthedocs. Moved to own issue #17
  • [x] Define TOC

[alexamici]

CONTRIBUTING is very light, but I'll close this issue for 0.9.0 release and open more specific issues for release 1.0.0.