Updated PR template (#1083)

Because we've set the merge queue to use the PR description as the
commit message to `main`, it's not good to start the PR template with a
commented block that PR makers don't have to remove. The new template
makes the checklist visible at the end and indicates it should be
deleted.

.github/PULL_REQUEST_TEMPLATE.md

@@ -1,18 +1,26 @@
-<!--
-⚠️ If you do not respect this template, your pull request will be closed.
-⚠️ Your pull request title should be short detailed and understandable for all.
-⚠️ Also, please add it in the CHANGELOG file under Unreleased section.
-⚠️ If your pull request fixes an open issue, please link to the issue.
+### Summary
 
-✅ I have added the tests to cover my changes.
-✅ I have updated the documentation accordingly.
-✅ I have read the CONTRIBUTING document.
--->
+Please describe what this PR changes as concisely as possible. Link to the issue(s) 
+that this addresses, if any.
 
-### Summary
+### Details and comments
 
+Some details that should be in this section include:
 
+- Why this change was necessary
+- What alternative solutions were considered and why the current solution was chosen
+- What tests and documentation have been added/updated
+- What do users and developers need to know about this change
 
-### Details and comments
+Note that this entire PR description field will be used as the commit message upon
+merge, so please keep it updated along with the PR. Secondary discussions, such as
+intermediate testing and bug statuses that do not affect the final PR, should be in the
+PR comments.
 
+### PR checklist (delete when all criteria are met)
 
+- [ ] I have read the contributing guide `CONTRIBUTING.md`.
+- [ ] I have added the tests to cover my changes.
+- [ ] I have updated the documentation accordingly.
+- [ ] I have added a release note file using `reno` if this change needs to be 
+      documented in the release notes.