Add new deployment notification of the production site

[tai271828]

It will be nice if we have deployment notification of the production site, because the development team is thriving. More and more cross-team members also contribute their code/commits to pycon.tw repository, and keep looking forward to their new features/requests land. An universal notification may be useful. The notification could be pushed/broadcasted via one of the following channel:

• internal slack
• telegram
• mailing list

The roadmap could be:

1. discuss/decide which channel(s) we are going to use
2. discuss/decide how we hook the notification