Introduce Swagger UI and the Swagger/OpenAPI specification. Explain
the structure of zulip.yaml and show examples of different sections
of the file.
This is a new file in /docs not yet included in the Read the Docs
table of contents. Where it should go should be determined as we iterate
on the Swagger UI integration and expand REST API doc coverage using it.
For more on Swagger UI and how Zulip uses it, see:
https://github.com/zulip/zulip/issues/3474https://github.com/zulip/zulip/pull/3397
With some minor tweaks to advertise this by tabbott.
Feorlen
Yago González