feat: Realtime schema updated in README

[emmambd]

Based on the discussion in issue #36, this is the updated schema that will be shared in the README.

[maximearmstrong]

Some comments in-line before approval.

I strongly suggest that we add a Type column right after the Field column. We can use the types described at gtfs.org.

We will also need the JSON type in some cases. For example, the type for a realtime URL would be JSON, and it would follow its own data structure, like GTFS Realtime URL data structure, which can be referenced in the Description column for the row. You could define this in another table in a subsection with direct_download_url, license_url, etc. The [Transitfeeds] API (https://transitfeeds.com/api/swagger/) follows this idea and works well.

I think it would make the data structure clearer and also avoid duplicates.

[barbeau]

Thanks @emmambd, some comments in-line.

[maximearmstrong]

A few things to consider before modifying the JSON schema :) Let's discuss them.

[maximearmstrong]

One small change to make :) Aside that, LGTM!

[emmambd]

@maximearmstrong Thanks for the update - should be set now!