add issue template for improvement / feature (#406)

Author: JannikSt

.github/ISSUE_TEMPLATE/feature_or_improvement.md

@@ -0,0 +1,16 @@
+---
+name: Feature / Improvement
+about: Request new features or improvements
+title: ''
+labels: enhancement
+assignees: ''
+---
+
+## Description
+<!-- What do you want and why? -->
+
+## Proposed Solution
+<!-- How should it work? -->
+
+## Additional Context
+<!-- Optional: Screenshots, examples, etc. -->