PULL_REQUEST_TEMPLATE.md

First of all, thanks for your contribution! :-)

Please makes sure these boxes are checked before submitting your PR, thank you!

• Make sure you follow antd's code convention.
• Run npm run lint and fix those errors before submitting in order to keep consistent code style.
• Rebase before creating a PR to keep commit history clear.
• Add some descriptions and refer relative issues for you PR.