Create CONTRIBUTING.md

.github/CONTRIBUTING.md

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+# Contributing
+
+When contributing to this repository, please first discuss the change you wish to make via issue,
+email, or any other method with the owners of this repository before making a change. 
+
+Please note we have a code of conduct, please follow it in all your interactions with the project.
+
+## Pull Request Process
+
+1. Ensure any install or build dependencies are removed before the end of the layer when doing a 
+   build.
+2. Update the README.md with details of changes to the interface, this includes new environment 
+   variables, exposed ports, useful file locations and container parameters.
+3. Increase the version numbers in any examples files and the README.md to the new version that this
+   Pull Request would represent. The versioning scheme we use is [SemVer](http://semver.org/).
+4. You may merge the Pull Request in once you have the sign-off of two other developers, or if you 
+   do not have permission to do that, you may request the second reviewer to merge it for you.
+
+(adapted from [this template](https://gist.github.com/PurpleBooth/b24679402957c63ec426))