Docs: Add contributing info

CONTRIBUTING.md

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+# Contributing
+
+## Issues
+
+Issues are always very welcome.
+
+### Tell us
+
+* What you are doing?
+  * Post sample use case that reproduces the issue. Attaching the entire Dockerfile is the best option
+* What do you expect to happen?
+* What is actually happening?
+
+When you post code, please use [Github flavored markdown](https://help.github.com/articles/github-flavored-markdown), in order to get proper syntax highlighting!
+
+## Pull requests
+
+Open a PR to the `develop` branch with your contribution.
+
+## Coding Guidelines
+
+As part of the test process, all commit messages will be linted, and your PR will **not** be accepted if it does not pass linting.