docs(pull request template): initial version (#91)

### What are you trying to accomplish?

Closes #80

### What approach did you choose and why?

I followed what was written in
https://docs.github.com/en/communities/using-templates-to-encourage-useful-issues-and-pull-requests/creating-a-pull-request-template-for-your-repository
and opted for the simplest route by adding the template to `.github/`.

### What should reviewers focus on?

Correctness 😉

.github/pull_request_template.md

@@ -0,0 +1,10 @@
+<!--
+  This pull request template provides suggested sections for framing your work.
+  You're welcome to change or remove headers if it doesn't fit your use case. :) 
+-->
+
+### What are you trying to accomplish?
+
+### What approach did you choose and why?
+
+### What should reviewers focus on?