update::pr_template::add one more bullet point

add one more bullet point to check the layout locally before ask someone to review

Author: nsuthison

.github/PULL_REQUEST_TEMPLATE.md

@@ -5,6 +5,7 @@
 - [ ] The PR is involve only 1 chapter at most.
 - [ ] The PR title conforms to the recommended [templates](https://github.com/rust-lang-th/book-th/blob/master/CONTRIBUTING.md#commit-message).
 - [ ] The PR has short description about what you has been done
+- [ ] Please make sure the layout of the page after you translate looks fantastic by checking from [running the book locally.](https://github.com/rust-lang-th/book-th#building)
 
 Change detail:
 <!-- Please add the PR description here -->