Add issue template

.github/ISSUE_TEMPLATE.md

+<!--
+If you want to request a feature or ask a question, feel free to remove all the irrelevant text.
+-->
+
+### System:
+
+- Operating System:
+- Qt version:
+- C++ compiler:
+- Desktop Environment: <!-- for Linux -->
+
+### Actual behavior
+
+### Expected behavior
+
+### Steps to reproduce
+
+<!-- If the program crashed. -->
+### Debugger traceback