[Apache][Infra] Committer: How to bind GitHub account to Apache account

1. Enable github 2FA:
https://docs.github.com/en/authentication/securing-your-account-with-two-factor-authentication-2fa/configuring-two-factor-authentication

2. Login apache gitbox: https://gitbox.apache.org/boxer/

3. Accept the invitation to join the apache team on GitHub: https://github.com/apache/

4. Linked successfully:

**NOTE**:
PPMC need to subscribe to the private mailing list. Please subscribe to private@graphar.apache.org by sending an email to private-subscribe@graphar.apache.org or by [subscribe helper]( https://whimsy.apache.org/committers/subscribe) with your `apache.org` suffix email.

Reference:
- https://infra.apache.org/apache-github.html
- https://cn.dubbo.apache.org/en/docs/contribution-guidelines/committer/new-committer-guide_dev/
- https://docs.github.com/en/authentication/securing-your-account-with-two-factor-authentication-2fa/configuring-two-factor-authentication

No repository file or test is named. Start with the Apache Infra and GitHub reference links, then locate the appropriate contributor or committer documentation and assess where these account-binding steps belong. Done means the guide accurately covers 2FA, Gitbox, the Apache team invitation, successful linking, and the private mailing-list subscription.

Written by the indexing model from the issue text.