the `-D` deletes a branch even if it is not merged. Might you also want to mention what happens if a PR was successfully merged? I tend to do
```
git fetch upstream
git checkout placeholder
git rebase upstream/master
git branch -d my-successfully-merged-branch
```
but possibly it is easier to tell people to just delete the branch on `github` (which it allows you to do when the PR is merged and then somehow pull this in [I wouldn't know how...])