Added docker-compose.yml

[latetedemelon]

Should now work better "out of the box". Testing still required.

[vdbg]

Sorry for the late review; just came back from vacation where I had no Internet access. Some general comments:

• Adding another method (env based + docker compose) is a great idea, but we shouldn't remove the ability to have influx and grafana in separate docker images. I have 1 influx with a dozen docker containers writing to it, and 1 grafana with 20+ dashboards unrelated to resmed. So this should be an "in addition to" vs. an "instead of"
• We shouldn't break backwards compatibility for the config. There are existing users of this package that use the config file. Logic should be: read config file if exists, then read environment variables if exist (patching the dictionary accordingly), then fail if sections missing. This way we can have the best of both worlds.
• The program shouldn't make (direct) filesystem modifications. Writes should be limited to logs and sending stuff to influx.

[vdbg]

This PR adds support for environment variables, and removes the requirement for a config file, without breaking backwards compatibility.

Feel free to update your PR to add docker compose functionality with updated instructions

[vdbg]

@latetedemelon : the changes to add env var support are in