Add documentation to modify lightcrawler-config.json

[mgifford]

There is a lightcrawler-config.json but too me a while to get to the architecture doc to learn how to configure it. A link here might be good:
https://github.com/GoogleChrome/lighthouse/blob/master/docs/architecture.md

Maybe there is a better one.

[mgifford]

I'm circling back to this as I came across this again.

The JSON output is interesting, but having something in HTML would be a lot easier to act on.