Add issue template

.github/issue_template.md

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+The Joda-Time project has been running for many years now, and the codebase is stable.
+As such, there are few things worthy of being raised as an issue.
+
+**As a general rule, you should raise a question at Stack Overflow, not here.**
+
+Before raising an issue, please check the [FAQs](http://www.joda.org/joda-time/faq.html).
+Please also search Stack Overflow and the issue history at GitHub.
+In particular, if the issue is Android specific, you are unlikely to get any assistance here.
+Please bear in mind that I've worked on Joda-Time in my spare time, unpaid, for over 15 years.
+As such, issue response time is likely to be slow.
+
+In the unlikely event you still think you've found an issue, please delete the text above and describe the problem as follows:
+
+### Key information
+
+- Joda-Time version
+- Result of `TimeZone.getDefault()`
+- Result of `DateTimeZone.getDefault()`
+
+### Problem description
+
+### Test case