Merge pull request #644 from jupyter/github-community

[ci skip] Fill out github community files

CODE_OF_CONDUCT.md

+Please see the [Project Jupyter Code of Conduct](https://github.com/jupyter/governance/blob/master/conduct/code_of_conduct.md).
\ No newline at end of file

CONTRIBUTING.md

+Thanks for for contributing! Please see the [Contributor Guide](https://jupyter-docker-stacks.readthedocs.io) in the 
+documentation for information about how to contribute [package updates](http://jupyter-docker-stacks.readthedocs.io/en/latest/contributing/packages.html),
+[recipes](http://jupyter-docker-stacks.readthedocs.io/en/latest/contributing/recipes.html),
+[tests](http://jupyter-docker-stacks.readthedocs.io/en/latest/contributing/tests.html),
+[features](http://jupyter-docker-stacks.readthedocs.io/en/latest/contributing/features.html),
+and [community-maintained stacks](http://jupyter-docker-stacks.readthedocs.io/en/latest/contributing/stacks.html).