Add contribution guidelines

CONTRIBUTING.md

@@ -0,0 +1,15 @@
+# Issues and Contributing
+
+Please note that only issues related to this Docker image will be addressed here.
+
+* If you have Docker related issues, please ask in the [Docker user mailing list](https://groups.google.com/forum/#!forum/docker-user).
+* If you have Jenkins related issues, please ask in the [Jenkins mailing lists](https://jenkins-ci.org/content/mailing-lists).
+* If you are not sure, then this is probably not the place to create an issue and you should use any of the previously mentioned mailing lists.
+
+If after going through the previous checklist you still think you should create an issue here please provide:
+
+* Docker commands that you execute
+* Actual result
+* Expected outcome
+* Output of `docker version`
+* Other relevant information