doc: add descriptions of state properties
Fixes: https://github.com/nodejs/node/issues/15268
Checklist
-
documentation is changed or added -
commit message follows commit guidelines
Affected core subsystem(s)
doc, http2
Do not update/delete: Banner broadcast message test data
Do not update/delete: Notification broadcast message test data
Fixes: https://github.com/nodejs/node/issues/15268
doc, http2