Create CONTRIBUTING.md (#1575)

https://github.com/fonttools/fonttools/community says fonttools doesn't have a contrib file, so I added one

CONTRIBUTING.md

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+## How to Contribute
+
+FontTools development is on-going in an active community of developers, that includes professional developers employed at major software corporations and at type foundries, as well as hobbyists.
+
+The project is run on Github, in the typical free/libre/open-source software way. 
+If you are unfamiliar with that, check out [opensource.guide](https://opensource.guide) and [producingoss.com](http://producingoss.com).
+
+We use Github's Issue Tracker to report, discuss and track bugs, map out future improvements, set priorities, and self-assign issues.
+If you find a bug, have an idea for a new feature, then please [create a new issue](https://github.com/fonttools/fonttools/issues) and we'll be happy to work with you on it!
+
+If you have a question or want to discuss usage from an end-user perspective, there is a mailing list at [groups.google.com/d/forum/fonttools](https://groups.google.com/d/forum/fonttools) mailing list.
+
+If you would like to speak to someone directly, you can also email the project lead, Behdad Esfahbod, privately at <behdad@behdad.org>
+
+If you make a pull request, you (or the organization that owns your copyrights) should be listed in the [README](https://github.com/fonttools/fonttools#copyrights).
+
+(There is also a development [groups.google.com/d/forum/fonttools-dev](https://groups.google.com/d/forum/fonttools-dev) mailing list for Continuous Integration notifications.)
+
+## Code reviews
+
+All submissions, including submissions by project members, go through a review process using GitHub Pull Requests.
+Consult [GitHub Help](https://help.github.com/articles/about-pull-requests/) for more information on making Pull Requests.
+
+## Code of Conduct
+
+This project has a [CODE_OF_CONDUCT.md](CODE_OF_CONDUCT.md)