Change the first heading in the pull request template to be useful

[mcdonnnj]

💡 Summary

Per #28 (review):

One thing I would like to see addressed is the octothorpe-wrapped comment at the very top of the PR template. All that line does is add a pointless horizontal line at the top of the PR, which I find maddening. We can't just remove the octothorpes, since then the linters complain that the first heading in the file isn't a first-level heading. We need to do one of the following:

• Add something to that first-level heading, but I can't think of anything meaningful. The PR title is already handled by the PR web page, so it doesn't make sense to put it there.
• Make the other headings all first-level headings, but that looks terrible.

Motivation and context

As the above remarks, the empty first heading in the pull request template is functionally useless at present.