meta: modify pull request template for prepending

The GitHub interface for new pull requests has started prepending
commit messages for single-commit pull requests. It had previously
been appending them. Modify the GitHub template to accommodate the new
behavior.

PR-URL: nodejs#10484
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Gibson Fahnestock <gibfahn@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Prince John Wesley <princejohnwesley@gmail.com>
Reviewed-By: Сковорода Никита Андреевич <chalkerx@gmail.com>
Reviewed-By: Sam Roberts <vieuxtech@gmail.com>
Reviewed-By: Myles Borins <myles.borins@gmail.com>

.github/PULL_REQUEST_TEMPLATE.md

@@ -1,5 +1,6 @@
 <!--
-Thank you for your pull request. Please review below requirements.
+Thank you for your pull request. Please provide a description above and review
+the requirements below.
 
 Bug fixes and new features should include tests and possibly benchmarks.
 
@@ -16,7 +17,3 @@ Contributors guide: https://github.com/nodejs/node/blob/master/CONTRIBUTING.md
 
 ##### Affected core subsystem(s)
 <!-- Provide affected core subsystem(s) (like doc, cluster, crypto, etc). -->
-
-
-##### Description of change
-<!-- Provide a description of the change below this comment. -->