Add docs for PurpleAir integration (#24943)

Co-authored-by: Franck Nijhof <frenck@frenck.nl>

source/_integrations/purpleair.markdown

@@ -0,0 +1,19 @@
+---
+title: PurpleAir
+description: Instructions on how to integrate PurpleAir sensors with Home Assistant.
+ha_category:
+  - Sensor
+ha_iot_class: Cloud Polling
+ha_release: 2023.1
+ha_codeowners:
+  - '@bachya'
+ha_domain: purpleair
+ha_platforms:
+  - sensor
+ha_integration_type: device
+ha_config_flow: true
+---
+
+[PurpleAir](https://www2.purpleair.com/) makes sensors that measure hyper-local air quality data and share it with the public.
+
+{% include integrations/config_flow.md %}