appt-book to 4

per https://chat.fhir.org/#narrow/stream/179159-cds-hooks/topic/hook.20maturity.20--.20request.20for.20implementer.20feedback!
[4 - Documented](../../specification/current/#hook-maturity-model)

Author: isaacvetter

docs/hooks/appointment-book.md

@@ -4,7 +4,7 @@
 | ---- | ----
 | specificationVersion | 1.0
 | hookVersion | 1.0
-| hookMaturity | 1 - Submitted
+| hookMaturity | [4 - Documented](../../specification/current/#hook-maturity-model)
 
 ## Workflow