chore: add PR template (#111)

Author: fmalcher

pull_request_template.md

@@ -0,0 +1,6 @@
+## Checklist for logo submission
+
+- [ ] Logo file added to the `logos` folder
+- [ ] Created a new entry in `metadata.json` (only `name` is mandatory)
+- [ ] Logo is an SVG with vector paths (no embedded pixel image)
+- [ ] The logo fills the image and there is no white margin (please remove the white margin if there is any 🙂 )