chore: add GitHub a pull request template (#911)

Author: yusukebe

.github/pull_request_template.md

@@ -0,0 +1,6 @@
+### The author should do the following, if applicable
+
+- [ ] Add tests
+- [ ] Run tests
+- [ ] `yarn changeset` at the top of this repo and push the changeset
+- [ ] Follow [the contribution guide](https://github.com/honojs/middleware?tab=readme-ov-file#how-to-contribute)