Update issue templates

.github/ISSUE_TEMPLATE/issue-template.md

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+---
+name: Issue template
+about: Issue template
+title: ''
+labels: ''
+assignees: ''
+
+---
+
+<!-- Please describe the issue in detail here, and fill in the fields below -->
+
+### Reproducing code example:
+
+<!-- A short code example that reproduces the problem/missing feature. It should be
+self-contained, i.e., possible to run as-is via 'python myproblem.py' -->
+
+```python
+import gklearn
+<< your code here >>
+```
+
+<!-- Remove these sections for a feature request -->
+
+### Error message:
+
+<!-- Full error message, if any (starting from line Traceback: ...) -->
+
+### graphkit-learn/Python version information:
+
+<!-- Output from 'import sys, gklearn; print(gklearn.__version__, sys.version)' -->