Modified the PR template to include README.md update reqirement if necessary

Author: bgorski

.github/PULL_REQUEST_TEMPLATE.md

@@ -67,3 +67,4 @@ https://github.com/magento/magento2ce/pull/<related_pr>
  - [ ] All commits are accompanied by meaningful commit messages
  - [ ] All new or changed code is covered with unit/integration tests (if applicable)
  - [ ] All automated tests passed successfully (all builds are green)
+ - [ ] README.md files for modified modules are updated and included in the pull request if any [README.md predefined sections](https://github.com/magento/devdocs/wiki/Magento-module-README.md) require an update