Docs for new Ruuvi Gateway integration (#25480)

Co-authored-by: J. Nick Koston <nick@koston.org>

source/_integrations/ruuvi_gateway.markdown

@@ -0,0 +1,31 @@
+---
+title: Ruuvi Gateway
+description: Support for Ruuvi Gateway devices acting as BLE remote scanners.
+ha_category:
+  - Sensor
+ha_release: '2023.2'
+ha_iot_class: Local Polling
+ha_config_flow: true
+ha_codeowners:
+  - '@akx'
+ha_domain: ruuvi_gateway
+ha_dhcp: true
+ha_integration_type: integration
+---
+
+Integrates [Ruuvi Gateway](https://ruuvi.com/gateway/) devices as
+polling BLE remote scanners [via the `/history` endpoint][poll].
+
+## Setup
+
+Make sure to [enable Bearer Token authentication][poll] on the Ruuvi Gateway device
+(and take note of the token).
+
+You may also wish to enable scanning for _all_ BLE beacons (not just RuuviTags);
+be sure to set the "Use Ruuvi Cloud or/and a custom server and configure more settings"
+option on the Cloud Options setup page, and when you get to the "Bluetooth Scanning" page,
+select "All (including third party beacons)".
+
+{% include integrations/config_flow.md %}
+
+[poll]: https://docs.ruuvi.com/gw-examples/polling-mode