github: put description of PR to the end of tmpl

[indutny]

Pull Request check-list

Please make sure to review and check all of these items:

• Does make -j8 test (UNIX) or vcbuild test nosign (Windows) pass with
  this change (including linting)?
• Is the commit message formatted according to CONTRIBUTING.md?
• If this change fixes a bug (or a performance problem), is a regression
  test (or a benchmark) included?
• 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.

Affected core subsystem(s)

Please provide affected core subsystem(s) (like buffer, cluster, crypto, etc)

Description of change

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.

NOTE: I had to manually re-order this to put Description of change to the bottom in this PR

[indutny]

cc @nodejs/collaborators @Fishrock123 @mscdex and all others.

[mscdex]

Now that I can see it rendered, can this line be moved to the end of the previous line?

[indutny]

@mscdex it will go over 80 columns, perhaps I should move afterwards / to the next line instead?

[indutny]

@mscdex hopefully, ack

[Fishrock123]

LGTM. Perhaps in a separate PR I'd like to not that checklist items that do not apply can be removed. (i.e. doc changes, example: #5391)

[indutny]

Landed in 4bd8b20, thank you! Please feel free to open follow-up PR.