Updates to airport-format.md

[erikquinn]

• arrivalRunway

• departureRunway

• restricted

• airways

• note that empty draw sections must be empty 2D, not just 1: [[]], not []

[ij1]

There's also lack of whitespace in "runways":[ in airport-format.md that would be nice to take care of once the documentation gets updated.

[n8rzz]

I'm not sure we need whitespace in the runways block. If anything, we need less of it.

I may be in the minority with that opinion though.

All the json files get minified for production anyway, so it's really a moot point for me. Whatever you guys want to do.