[Minor] Add github issue template

.github/ISSUE_TEMPLATE.md

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+### Classification (Please choose *one* option):
+
+* [x] Crash/Hang/Data loss
+* [ ] WebUI/Usability
+* [ ] Serious bug
+* [ ] Other bug
+* [ ] Feature
+* [ ] Enhancement
+
+### Reproducibility (Please choose *one* option):
+
+* [X] Always
+* [ ] Sometimes
+* [ ] Rarely
+* [ ] Unable
+* [ ] I didn’t try
+* [ ] Not applicable
+
+### Rspamd version:
+
+### Operation system, CPU, memory and environment:
+
+### Description (Please provide a descriptive summary of the issue):
+
+### Compile errors (if any):
+
+### Steps to reproduce:
+
+### Expected results:
+
+### Actual results:
+
+### Debugging information (See https://rspamd.com/doc/faq.html#how-to-figure-out-why-rspamd-process-crashed):
+
+### Configuration:
+
+### Additional information: