Merge pull request #655 from dean0x7d/issue-template

Add a GitHub issue template

ISSUE_TEMPLATE.md

+Make sure you've completed the following steps before submitting your issue -- thank you!
+You can remove this template text afterward.
+
+1. Check if your question has already been answered in the [FAQ](http://pybind11.readthedocs.io/en/latest/faq.html) section.
+2. Make sure you've read the [documentation](http://pybind11.readthedocs.io/en/latest/). Your issue may be addressed there.
+3. If those resources didn't help and you only have a short question (not a bug report), consider asking in the [Gitter chat room](https://gitter.im/pybind/Lobby).
+4. If you have a genuine bug report or a more complex question which is not answered in the previous items (or not suitable for chat), please fill in the details below.
+5. Include a self-contained and minimal piece of code that reproduces the problem. If that's not possible, try to make the description as clear as possible.
+
+
+#### Issue description
+
+(Provide a short description, state the expected behavior and what actually happens.)
+
+#### Reproducible example code
+
+(The code should be minimal, have no external dependencies, isolate the function(s) that cause breakage. Submit matched and complete C++ and Python snippets that can be easily compiled and run to diagnose the issue.)