Create CONTRIBUTING.rst

CONTRIBUTING.rst

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+Contributing to Mars
+====================
+
+Reporting bugs and asking questions
+-----------------------------------
+
+We use `GitHub issues`_ for bug reports and feature requests. For discussions
+about development, questions about usage, or any general questions, we use our
+mailing list `mars-dev@googlegroups.com`_.
+
+To contribute a patch:
+----------------------
+
+1. Break your work into small, single-purpose patches if possible. It's much
+   harder to merge in a large change with a lot of disjoint features.
+2. Submit the patch as a GitHub pull request against the master branch.
+3. Make sure that your code passes the unit tests.
+4. Add new unit tests for your code.
+
+.. _`GitHub issues`: https://github.com/mars-project/mars/issues
+.. _`mars-dev@googlegroups.com`: https://groups.google.com/forum/#!forum/mars-dev