core/pr-review.md - Don't assume that `git`==`hub`

The example command works if you've manually installed the `hub` with all
the suggestions in upstream's guide -- specifically, they suggest aliasing
`git`==`hub`.  However, in `civi-download-tools`, we download the `hub`
command but can't setup the alias.

Documenting commands as `hub <foo>` should make them more robust/portable to
more configurations.