DOC: Create ISSUE_TEMPLATE.md

Create an `ISSUE_TEMPLATE.md` file to provide a guide when submitting issues to ITK.

Change-Id: I0828b37f5999fe1d2acb59885c0ba1dc648b5d67

ISSUE_TEMPLATE.md

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+[Before submitting an issue, please check that your issue hasn't been already
+filed]
+
+### Description
+
+[Description of the issue]
+
+### Steps to Reproduce
+
+1. [First Step]
+2. [Second Step]
+3. [and so on...]
+
+[Provide a minimal, compilable code snippet (either through a
+[GitHub gist](https://gist.github.com/) or your own files reproducing the issue
+if necessary]
+
+### Expected behavior
+
+[What you expect to happen]
+
+### Actual behavior
+
+[What actually happens]
+
+### Reproducibility
+
+[What percentage of the time does it reproduce?]
+
+### Versions
+
+[If a tagged version, you can get this information by inspecting the
+`ITK_VERSION_MAJOR` `ITK_VERSION_MINOR` and `ITK_VERSION_PATCH` variable
+values in the `ITKConfig.cmake` file]
+
+[If the commit number is required, run `$ git rev-parse --short HEAD`]
+
+### Environment
+
+[Which your OS and compiler are]
+
+### Additional Information
+
+[Any additional information, configuration or data that might be necessary to reproduce the issue.]
+
+
+Note: Use issues for their purpose; isses are not for code help. Need help? Ask
+your question at [https://discourse.itk.org/](https://discourse.itk.org/)