Mention @somebody. They’re notified.

Ever wish you could summon a particular someone to take a look at an issue or
pull request? Now you can:

When you @mention a GitHub username anywhere
in the context of an issue or pull request, that person is notified and
subscribed to future updates.

Better Notification Controls

You can also now manage notification settings at the individual issue or pull
request level. This lets you manually subscribe to any issue without commenting,
or unsubscribe from issues no longer relevant to your interests:

Disabling @mention Notifications

Would you rather not be notified when mentioned? Disable
@mention notifications in the
Notification Center
under Account Settings: