Describe the feature or problem you’d like to solve

People who installed GitHub CLI from the brew install gh command don't get notified that there's an update. We expect that many people are still on older versions without even realizing there's a new one available.

Proposed solution

We'd like to include an update notifier for people who have installed gh via the official homebrew package.

Because there's a delay between when we publish a release and when it gets deployed to homebrew-core, let's add a 24 hour delay before the update notification appears. Ideally, it would be great to include as part of the notification "brew upgrade gh" so people know immediately how to upgrade. Obviously this would necessitate that we detect that it's a homebrew installation and only display that message there.