Create PULL_REQUEST_TEMPLATE.md (#304)

Author: wuweiweiwu

PULL_REQUEST_TEMPLATE.md

@@ -0,0 +1,13 @@
+Thanks for contributing to react-split-pane!
+
+**Before submitting a pull request,** please complete the following checklist:
+
+- [ ] The existing test suites (`yarn test`) all pass
+- [ ] For any new features or bug fixes, both positive and negative test cases have been added
+- [ ] For any new features, documentation has been added
+- [ ] For any documentation changes, the text has been proofread and is clear to both experienced users and beginners.
+- [ ] Format your code with [prettier](https://github.com/prettier/prettier) (`npm run prettier`).
+
+Here is a short checklist of additional things to keep in mind before submitting:
+* Please make sure your pull request description makes it very clear what you're trying to accomplish. If it's a bug fix, please also provide a failing test case (if possible). In either case, please add additional unit test coverage for your changes. :)
+* Be sure you have notifications setup so that you'll see my code review responses. (I may ask you to make some adjustments before merging.)