Add docs for Guardian valve implementation (#30693)

source/_integrations/guardian.markdown

@@ -8,6 +8,7 @@ ha_category:
   - Button
   - Sensor
   - Switch
+  - Valve
 ha_config_flow: true
 ha_codeowners:
   - '@bachya'
@@ -19,6 +20,7 @@ ha_platforms:
   - diagnostics
   - sensor
   - switch
+  - valve
 ha_dhcp: true
 ha_integration_type: device
 ---
@@ -31,7 +33,8 @@ There is currently support for the following device types within Home Assistant:
 - **Binary sensor**: reports the status of the onboard leak detector and access point
 - **Button**: add various configuration controls
 - **Sensor**: reports on the device's detected temperature and uptime
-- **Switch**: allows the user to open and close the valve
+- **Switch**: allows the user to enable and disable the onboard access point
+- **Valve**: allows the user to open and close the valve
 
 {% include integrations/config_flow.md %}