docs: add contribution guidelines

Author: codesenberg

docs/CONTRIBUTING.md

@@ -0,0 +1,6 @@
+### Contribution Guidelines
+For relevant info on how to format commit messages and check the code before submitting pull requests see [PULL_REQUEST_TEMPLATE](https://github.com/codesenberg/bombardier/blob/master/.github/PULL_REQUEST_TEMPLATE.md).
+
+### Reporting issues
+Please open an issue if you would like to discuss anything that could be improved, have a suggestion or want to report a bug.
+In latter case refer to [ISSUE_TEMPLATE](https://github.com/codesenberg/bombardier/blob/master/.github/ISSUE_TEMPLATE.md).