Add incompatibility issue template

.github/ISSUE_TEMPLATE/report-incompatibility.md

@@ -0,0 +1,16 @@
+---
+name: Report incompatibility
+about: Report an incompatibility between RustPython and CPython
+title: ''
+labels: feat
+assignees: ''
+
+---
+
+## Feature
+
+<!-- What Python feature is missing from RustPython? Give a short description of the feature and how you ran into its absence. -->
+
+## Python Documentation
+
+<!-- Give a link to the feature in the CPython documentation (https://docs.python.org/3/) in order to assist in its implementation. -->