docs(air-quality): note the pm, temperature and humidity readings need homebridge 2.5.1

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Author: bwp91

CHANGELOG.md

@@ -12,6 +12,7 @@ All notable changes to `@homebridge-plugins/homebridge-matter` will be documente
 - fix(light-sensor): use matter's lux scale, which adds 1, and send 0 below 1 lux
 - fix(colour-light): convert xy colour with matter's 65536 scale
 - fix(venetian-blind): declare an interior venetian blind, not a sheer shade
+- docs(air-quality): note the pm, temperature and humidity readings need homebridge 2.5.1
 
 ## v1.8.0 (2026-11-01)
 

src/devices/AirQualitySensorAccessory.ts

@@ -48,6 +48,11 @@ export class AirQualitySensorAccessory extends BaseMatterAccessory {
 
         // Note: the only cluster that appears in the Home app is the Air Quality cluster.
         // The other measurements can be accessed by other Matter-compatible apps.
+        //
+        // These readings are optional clusters, and Homebridge v2.5.1 and later
+        // add them from the state declared here. Before that they were left
+        // off the device without an error, and every later update failed.
+        // A reading needs measurementUnit and measurementMedium.
 
         // PM2.5 - Fine particulate matter (≤2.5 micrometers)
         // Values in µg/m³ (micrograms per cubic meter)