Add GitHub pull request template

- Create structured PR template with What/Why/Changes/Testing sections
- Include checklist for changeset and README updates
- Auto-loaded by GitHub when creating pull requests

Author: polRk

.github/pull_request_template.md

@@ -0,0 +1,25 @@
+## What
+
+<!-- Brief description of what this PR does (one sentence) -->
+
+## Why
+
+<!-- Why this change is needed. What problem does it solve? -->
+
+## Changes
+
+## <!-- List of main changes -->
+
+-
+-
+
+<!-- Breaking changes (if any) -->
+
+## Testing
+
+<!-- What tests were added/updated and how to verify the changes work -->
+
+## Checklist
+
+- [ ] Changeset added (if package changes)
+- [ ] README updated (if public API changed)