Update ISSUE_TEMPLATE.md

Author: bkrem

.github/ISSUE_TEMPLATE.md

@@ -1,3 +1,26 @@
-- [ ] Implementation
-- [ ] Unit test
-- [ ] Docs
+Thank you for taking the time to report an issue with react-d3-tree!  
+
+Feel free to delete any questions that do not apply.
+
+## Are you reporting a bug, or opening a feature request?
+[Replace with your answer]
+
+* Please insert below the code you are checking with mypy,
+  or a mock-up repro if the source is private. We would appreciate
+  if you try to simplify your case to a minimal repro.
+  
+  
+## What is the actual behavior/output?
+[Replace with your answer if relevant]
+
+## What is the behavior/output you expect?
+[Replace with your answer if relevant]
+
+## Can you consistently reproduce the issue/create a reproduction case (e.g. on https://codesandbox.io)?
+[Replace with your answer if relevant]
+
+## What version of react-d3-tree are you using?
+[Replace with your answer]
+
+## If react-d3-tree crashed with a traceback, please paste the full traceback below.
+[Replace with your traceback]