[Idea] Make it more convenient way to get the invite code

[Simon-Laux]

Currently you need to look into the docker logs, where the link can be hard to find (sometimes you first need to find out the container id, because the alias does not in every scenario).

Improvement ideas:
A) suggest a command in documentation, that includes a pipe to grep to find it faster
B) make fake conversation where the bot sends it on first setup (or when it changes, when changing bit email address or key is possible)
C) or setup a canned response, which would serve the additional purpose to give people on other channels a fast way to get to know how to get-in-touch encrypted over delta chat.

Somewhat related to #19