github: put description of PR to the end of tmpl

It looks like github appends commit log right after the template
contents. Seeing this it does not look logical to ask for details first.

This commit puts `Description of change` part to the end of the
template.

PR-URL: #5378
Reviewed-By: Jeremiah Senkpiel <[email protected]>

Author: indutny

.github/PULL_REQUEST_TEMPLATE.md

@@ -1,7 +1,3 @@
-### Description of change
-
-_Please provide a description of the change here._
-
 ### Pull Request check-list
 
 _Please make sure to review and check all of these items:_
@@ -14,11 +10,15 @@ _Please make sure to review and check all of these items:_
 - [ ] Is a documentation update included (if this change modifies
   existing APIs, or introduces new ones)?
 
-_NOTE: these things are not required to open a PR and can be done afterwards /
-while the PR is open._
+_NOTE: these things are not required to open a PR and can be done
+afterwards / while the PR is open._
 
 ### Affected core subsystem(s)
 
 _Please provide affected core subsystem(s) (like buffer, cluster, crypto, etc)_
 
 [0]: https://github.com/nodejs/node/blob/master/CONTRIBUTING.md#step-3-commit
+
+### Description of change
+
+_Please provide a description of the change here._