templates: add some external tasks to the release checklist

These are not strictly part of the upstream release, but let's keep the
entire process in one place so nothing gets missed.

.github/ISSUE_TEMPLATE/release-checklist.md

@@ -51,4 +51,10 @@ Quay release:
  - [ ] Click the gear next to the tag, select "Add New Tag", enter `release`, and confirm
 
 Housekeeping:
+ - Update Butane package for the current RHCOS development release
+   - [ ] Update the dist-git repo, following the instructions above
+   - [ ] PR the changes
+   - [ ] When the PR lands, build the package
+ - [ ] File ticket similar to [this one](https://issues.redhat.com/browse/ART-3043) to sync the new version to mirror.openshift.com
+ - [ ] Ask bgilbert to update the [MacPorts package](https://github.com/macports/macports-ports/tree/master/sysutils/butane)
  - [ ] Vendor the new Butane version in [mantle](https://github.com/coreos/coreos-assembler/tree/main/mantle)