Update GitHub pull request template to align with issue template

.github/PULL_REQUEST_TEMPLATE.md

@@ -1,3 +1,26 @@
 <!--
-Thanks for contributing to Spring Boot. Please provide a brief description of your pull-request and reference any related issue numbers (prefix references with #).
--->
+Thanks for contributing to Spring Boot. Please review the following notes before
+submitting you pull request.
+
+Security Vulnerabilities
+
+STOP! If your contribution fixes a security vulnerability, please do not submit it.
+Instead, please head over to https://pivotal.io/security to learn how to disclose a
+vulnerability responsibly.
+
+Dependency Upgrades
+
+Please do not open a pull request for a straightforward dependency upgrade (one that
+only updates the version property). We have a semi-automated process for such upgrades
+that we prefer to use. However, if the upgrade is more involved (such as requiring
+changes for removed or deprecated API) your pull request is most welcome.
+
+Describing Your Changes
+
+If, having reviewed the notes above, you're ready to submit your pull request, please
+provide a brief description of the proposed changes. If they fix a bug, please
+describe the broken behaviour and how the changes fix it. If they make an enhancement,
+please describe the new functionality and why you believe it's useful. If your pull
+request relates to any existing issues, please reference them by using the issue number
+prefixed with #.
+-->