Add PR template (#298)

Author: huozhi

.github/pull_request_template.md

@@ -0,0 +1,28 @@
+<!--
+Thanks for opening a PR! Your contribution is much appreciated.
+In order to make sure your PR is handled as smoothly as possible we request that you follow the instructions below.
+
+
+### New page 📚
+
+- Created default English translation (`.en-US`) page
+- Add translation pages for all other languages (no need to translate them but copy from the original one)
+
+### Updating existing pages ✍️
+
+- Update it in all other languages if it's code example (Use English if you don't know how to translate)
+
+
+🎉🎉🎉 Thanks for your contribution! 🎉🎉🎉
+
+-->
+
+### Description
+
+<!-- What're you changing? -->
+
+- [ ] Adding new page
+- [ ] Updating existing documentation
+- [ ] Other updates
+
+