Review / Edit Technical Documents - GraphQL queries, how to download data, etc.

[liamphmurphy]

(Original issue pulled from here: trynmaps/metrics-mvp#571)

Original Description:
We have a few guides for our GraphQL API, and I think it's technically possible for the public to pull some of our raw data. But it's not very easy for 3rd party developers to access. We should make a public site (either part of this app, or on a Wiki on this repo) that gives data/API access instructions to developers.

For Our Purposes:
Looking at the repo's primary README, this issue made me think we could edit it to do a few things:

1. Since this repo is specific to TriMet, we could reduce clutter for onboarding by removing any references to non-Portland specific public transit systems (or perhaps documenting these elsewhere).
2. Provide examples of the kinds of GraphQL queries made from opentransit-metrics
3. Anything else that makes sense along these lines.