docs: Add GitHub bug report template

Nudge issue reporters into providing meaningful information, so that
we don't need to ask them for details every time.

.github/ISSUE_TEMPLATE/bug_report.md

@@ -0,0 +1,45 @@
+---
+name: Bug report
+about: Report a bug in tutor-contrib-retirement
+title: ''
+labels: ''
+assignees: ''
+
+---
+
+# Summary
+
+Replace this with a short summary (one sentence or short paragraph) of the issue you are seeing.
+
+## What I did
+
+Explain the steps you undertook that led to the unexpected behavior you are observing. Please include relevant documentation snippets, such as the `RETIREMENT_*` settings from Tutor’s `config.yml`.
+
+It’s OK to remove or mask credentials, but otherwise try to err on the side of sharing more rather than less information.
+
+## What I expected to happen
+
+Explain how you expected Tutor to behave with your configuration.
+
+## What actually happened
+
+Explain how Tutor behaved differently than you expected.
+
+## My environment
+
+Please add some information about the environment that you’re working in. At a minimum, include these items:
+
+* Tutor version: (Insert the Tutor version you are using.)
+* `tutor-contrib-retirement` version: (Insert the plugin version you are using. If you installed from Git, enter the tag or branch name, or the commit reference.)
+* Output of the retirement command/CronJob: (In Tutor local, this is the output of the `tutor local retire-users`. In Kubernetes, you can get the output by `kubectl -n <your-namespace> logs <retirement-pod-name>`)
+
+Additionally, you might also want to add any of the items below, if you think they might be relevant to the bug:
+
+* Kubernetes versions: (If you are reporting a bug that applies to deploying this plugin with `tutor k8s`, add your `kubectl version` output. Otherwise, remove this item.)
+* Docker/Podman version: (If you are running `tutor local`, the output of `docker version` might be relevant.)
+
+Make sure to redact any sensitive information regarding your users and products.
+
+## Additional context
+
+If there’s any other context you’d like to share, please add it here. Otherwise, you can delete this section.