Add Usb discovery (#19015)

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

source/_integrations/default_config.markdown

@@ -39,6 +39,7 @@ This integration is a meta-component and configures a default set of integration
 - [Tag](/integrations/tag/) (`tag`)
 - [Timer](/integrations/timer/) (`timer`)
 - [Updater](/integrations/updater/) (`updater`)
+- [USB](/integrations/usb/) (`usb`)
 - [Webhooks](/integrations/webhook) (`webhook`)
 - [Zero-configuration networking (zeroconf)](/integrations/zeroconf/) (`zeroconf`)
 - [Zone](/integrations/zone/) (`zone`)

source/_integrations/usb.markdown

@@ -0,0 +1,27 @@
+---
+title: USB Discovery
+description: Discover usb devices on the host.
+ha_category:
+  - Utility
+ha_iot_class: Local Push
+ha_release: 2021.9
+ha_domain: usb
+ha_quality_scale: internal
+ha_codeowners:
+  - '@bdraco'
+---
+
+The USB Discovery integration will watch the host for USB devices. Discovered integrations will show up in the discovered section on the integrations page in the configuration panel.
+
+- On Linux, devices are detected as soon as they are plugged in.
+
+- On Windows and Mac OS, devices are detected at startup and hourly.
+
+## Configuration
+
+This integration is by default enabled, unless you've disabled or removed the [`default_config:`](/integrations/default_config/) line from your configuration. If that is the case, the following example shows you how to enable this integration manually:
+
+```yaml
+# Example configuration.yaml entry
+usb:
+```