Default config values - Githubissues

This PR does:

Document default configuration options (extracted from: https://github.com/nodecg/nodecg/blob/master/src/server/config/loader.ts)
(as discussed on discord:) remove some legacy options
Implement Issue #11 (but in footer, as this was where there was the discord link already)
fix build command in Readme (also found a LOT of linting issues not related to my changes when trying to run mdl => will fix them in another PR)

nodecg / docs