This is a first iteration. I want to get feedback on a few aspects, so
starting from here as a baseline.

Set up matching the style of "Getting Started", except I kept the
headers inside the tabs for now as it makes for a useful right-hand TOC.

Add section for recommending enabling Hermes. Not sure of contents yet,
and still have to test.

Favor linking to original setup guide instead of repeating content.

They don't work correctly with the righthand TOC.

There was way too much yellow.

Because `xcodebuild clean` already failed me once when XCode GUI clean
worked.

Also standardize on using yarn scripts from template for commands, it's
a little confusing to see the mix of `npx` and `yarn` once we start
referring to `yarn pod-install`