Improve readme for contributors & self-hosting

[FlxMgdnz]

The root README has a Getting Started section that links you to the README for the backend, which is helpful if you want to run the backend on bare metal. However, most users probably don't want the hassle of trying to run everything on bare metal especially if they don't want to install Postgres/MySQL/Golang locally.

It's not immediately obvious there's a way to run the project entirely from Docker. The documentation on running the Docker stuff is in the deploy section, but this section doesn't appear to be advertised from the root README or the backend docs. I think it'll be good to add a point in the Getting Started section that there's a way to run the project entirely in Docker.

I would recommend the Getting Started section be formatted to offer two ways to run the project:

• Docker
• Bare Metal