Add Update entity description to Plex (#29248)

source/_integrations/plex.markdown

@@ -2,8 +2,10 @@
 title: Plex Media Server
 description: Instructions on how to integrate Plex into Home Assistant.
 ha_category:
+  - Button
   - Media Player
   - Sensor
+  - Update
 featured: true
 ha_release: 0.7.4
 ha_iot_class: Local Push
@@ -15,6 +17,7 @@ ha_platforms:
   - button
   - media_player
   - sensor
+  - update
 ha_zeroconf: true
 ha_integration_type: integration
 ---
@@ -27,6 +30,7 @@ There is currently support for the following device types within Home Assistant:
 
 - [Sensor](#sensor)
 - [Button](#button)
+- [Update](#update)
 - [Media Player](#media-player)
 
 If a Plex server has been claimed by a Plex account via the [claim interface](https://plex.tv/claim), Home Assistant will require authentication to connect.
@@ -136,6 +140,12 @@ play_plex_on_tv:
 
 {% endraw %}
 
+## Update
+
+Notifications of new releases of Plex Media Server are shown using an Update entity. Detailed release notes are provided.
+
+Automatic upgrades of Plex Media Server can be triggered for some installation types, such as Windows and certain NAS devices.
+
 ## Media Player
 
 The Plex media player platform will create Media Player entities for each connected client device. These entities will display media information, playback progress, and playback controls (if supported by the streaming device).