Determine and document default match parameters

[emilyeros]

Not sure if we have a generally agreed-upon set of matching parameters. We should set something that maximizes matches for a group of cities, surface that information, and provide discussion about edge cases and situations where cities may want to change a parameter.

The Getting Started with Shared Streets observable provides breadcrumbs for understanding this but we don't explicitly address it from the perspective of getting a city's base maps to match well. That content can go into the training posts.

Why we need this:

[morganherlocker]

This is changing substantially in 1.0, as we've seen in the alpha release. That said, we probably still want this for the OSRM relevant params, which are similar.