Update CONTRIBUTING.md

Add signpost for people creating new issues.

CONTRIBUTING.md

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+## About to create a new Github Issue?
+
+We appreciate that. But before you do, please learn our basic rules:
+
+* This is not a support forum. If you have a question, please go to [The Cukes Google Group](groups.google.com/group/cukes).
+* Do you have an idea for a new feature? Then don't expect it to be implemented unless you or someone else sends a [pull request](https://help.github.com/articles/using-pull-requests). You might be better to start a discussion on [the google group](groups.google.com/group/cukes).
+* Reporting a bug? Please tell us:
+  * which version of Cucumber you're using
+  * which version of Ruby you're using.
+  * How to reproduce it. Bugs with a failing test in a [pull requests](https://help.github.com/articles/using-pull-requests) get fixed much quicker. Some bugs may never be fixed.
+* Want to paste some code or output? Put \`\`\` on a line above and below your code/output. See [GFM](https://help.github.com/articles/github-flavored-markdown)'s *Fenced Code Blocks* for details.
+* We love [pull requests](https://help.github.com/articles/using-pull-requests). But if you don't have a test to go with it we probably won't merge it.
+
 # Contributing to Cucumber
 
 This document is a guide for those maintaining Cucumber, and others who would like to submit patches.