Added cal.com as template

[kunumigab]

Scheduling infrastructure for absolutely everyone.

Docker-Compose instructions used here: https://github.com/calcom/docker

[RayBB]

@kunumigab
Not a maintainer but two small bits of feedback based on what I've seen in this repo:

1. Usually the app service goes before the database service in the compose file (probably just so it's higher up when you edit variables)
2. Usually template files end with a newline

Unfortunately, I can't test this right now since my main server is ARM.

[RayBB]

@andrasbacsai any chance you could review this PR this week?
@kunumigab