Add new file

CONTRIBUTING.md

+Want to contribute? Great! First, read this page.
+
+### Code guidelines
+We expect all submissions to be properly formatted using gofmt.
+Golint and govet shall not complain about your code. Gocyclo shall not report 
+complexity above 15. And your code should not lower the testcoverage of our
+codebase.
+
+### Code reviews
+All submissions, including submissions by project members, require review. We
+use Gitlab merge requests for this purpose.
+
+### License
+By sending us your code you agree to release your contribution under the projects
+chosen license: BSD 3-Clause license (see LICENSE file).
\ No newline at end of file