Add Tailscale integration (#20325)

source/_integrations/tailscale.markdown

@@ -0,0 +1,31 @@
+---
+title: Tailscale
+description: Instructions on how to integrate Tailscale within Home Assistant.
+ha_category:
+  - Binary Sensor
+  - Network
+ha_release: 2021.12
+ha_iot_class: Cloud Polling
+ha_config_flow: true
+ha_codeowners:
+  - '@frenck'
+ha_domain: tailscale
+ha_platforms:
+  - binary_sensor
+ha_quality_scale: platinum
+---
+
+The Tailscale integration integrates the [Tailscale](https://www.tailscale.com) API
+with Home Assistant; giving you the possibility to monitor and automate on
+the state of the devices in your Tailscale VPN network (Tailnet).
+
+## Prerequisites
+
+To use the Tailscale integration, you will need to obtain an API key,
+you can create one in the [Tailscale Admin Panel](https://login.tailscale.com/admin/settings/authkeys).
+
+Additionally, you will need to know the Tailnet name of your Tailscale network.
+You can find it in the top left corner in the [Tailscale Admin Panel](https://login.tailscale.com/admin/settings/authkeys)
+(beside the Tailscale logo).
+
+{% include integrations/config_flow.md %}