update Running.md

[rcursaru]

clarify setup steps when using docker; use a single directory to hold all configuration for docker container

[kradalby]

Hi, thanks for the contribution, it looks sensible.

I am wondering if we should split the whole docker setup into a separate file as the current configuration reads really confusing and is very obtuse and hard to keep track of.

Would you be up for actually splitting it up into a "running in docker".md ?

Neither I nor @juanfont use docker for headscale, and because of that we are not the people to maintain the docker configuration/running guide.

[ohdearaugustin]

Looks good to me