Create bug template

.github/ISSUE_TEMPLATE/bug_report.md

+---
+name: Bug report
+about: Create a report to help us improve
+title: ''
+labels: ''
+assignees: ''
+
+---
+
+<!--
+**Note:**
+- Do not use the bug and feature tracker for support requests. Use the `cython-users` mailing list instead.
+- Did you search for similar issues already? Please do, it helps to save us precious time that we otherwise could not invest into development.
+-->
+
+**Describe the bug**
+A clear and concise description of what the bug is.
+
+**To Reproduce**
+Code to reproduce the behaviour:
+```cython
+```
+
+**Expected behavior**
+A clear and concise description of what you expected to happen.
+
+**Environment (please complete the following information):**
+ - OS: [e.g. Linux, Windows, macOS]
+ - Version [e.g. 0.29.18]
+
+**Additional context**
+Add any other context about the problem here.