slack-event-bb.team_added.js

// Send a message to the user that added the bot right after it connects
slapp.event('bb.team_added', function (msg) {
  slapp.client.im.open({ token: msg.meta.bot_token, user: msg.meta.user_id }, (err, data) => {
    if (err) {
      return console.error(err)
    }
    let channel = data.channel.id

    msg
      .say({ channel, text: 'Thanks for adding me to your team!' })
      .say({ channel, text: 'Please /invite me to a channel to get things started.' })
  })
})