[meta] Address remaining TAG review issues

[alexshalamov]

List of remaining issues for ALS TAG review.

• There's only a single example and no linked explainer document that would provide deeper understanding of how the various bits get used together. I think this would be clarifying both for the reader and the authors.

• The example (singular?) doesn't show how to use the Permission API in conjunction with the Ambient Light API, which seems pretty critical to actual use.

• Still not seeing an explainer/examples document in the Github repo (https://github.com/w3c/ambient-light). Should I be looking elsewhere for those?