Commenting the PR template so it's not included in PR messages by def…

…ault

This works as Markdown is just augmented raw HTML

.github/PULL_REQUEST_TEMPLATE.md

@@ -1,5 +1,7 @@
+<!--
 Thanks for contributing, you're awesome! :star:
 Please describe expected and observed behaviour, and what you're fixing.
 For visual fixes, please include tested browsers and screenshots.
 Search for related existing issues and link to them if possible.
-Please read https://docs.silverstripe.org/en/contributing/code/
+Please read https://docs.silverstripe.org/en/contributing/code/
+-->