Update issue template

.github/ISSUE_TEMPLATE.md

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+Thanks for raising an issue. Please read (and discard) the below:
+
+**Security Issue?** Please report responsibly via https://pivotal.io/security  
+_(Do not diclose here. It will be deleted!!)._
+
+**Questions:** Please use Stack Overflow.  
+
+**Issue vs Pull Request** Do not create both.  
+_(You can start with an issue, and submit a pull request later, superseding the issue)_
+
+**Bug Reports:** Specify affected versions and explain what your goal is.  
+_(A test case or isolated sample makes it easier for us to help)_
+
+**Enhancements:** Please describe the problem.  
+_(There may already be a solution, or a way to solve it you had not considered.)_