Initial CONTRIBUTING.md (#655)

CONTRIBUTING.md

@@ -0,0 +1,11 @@
+# Contributing
+Contributions to nnn are welcome! There's always an open issue with the current ToDo list, which contains the proposed features for the next release you can get your hands on. Any small changes or ideas should go in there, rather than in a separate issue.
+
+Before suggesting changes, please read a bit about [the design principles nnn follows](https://github.com/jarun/nnn/wiki#design), and make sure you aren't breaking any of them.
+
+## Resources
+The [wiki](https://github.com/jarun/nnn/wiki/Developer-guides) has some resources for developers you might be interested in: building, debugging...
+
+## Communication
+* [Gitter chat](https://gitter.im/jarun/nnn)
+* [GitHub team](https://github.com/nnn-devs) (if you plan on contributing regularly, ask for an invitation).