Add Rain Bird irrigation calendar documentation (#26151)

* Add Rain Bird calendar documentation

* tiny tweak

---------

Co-authored-by: c0ffeeca7 <38767475+c0ffeeca7@users.noreply.github.com>

source/_integrations/rainbird.markdown

@@ -3,6 +3,7 @@ title: Rain Bird
 description: Instructions on how to integrate your Rain Bird LNK WiFi Module within Home Assistant.
 ha_category:
   - Binary Sensor
+  - Calendar
   - Irrigation
   - Sensor
   - Switch
@@ -15,6 +16,7 @@ ha_codeowners:
 ha_domain: rainbird
 ha_platforms:
   - binary_sensor
+  - calendar
   - number
   - sensor
   - switch
@@ -26,6 +28,7 @@ This `rainbird` integration allows interacting with [LNK WiFi](https://www.rainb
 There is currently support for the following device types within Home Assistant:
 
 - [Binary Sensor](#binary-sensor)
+- [Calendar](#calendar)
 - [Number](#number)
 - [Switch](#switch)
 
@@ -40,6 +43,12 @@ will run when turning on a zone switch (default is 6 minutes). This can be overr
 
 The `rainsensor` sensor will tell if you if the device has detected rain.
 
+## Calendar
+
+Some Rain Bird devices support automatic irrigation schedules configured with the Rain Bird app.
+and are available in Home Assistant as a [Calendar](https://www.home-assistant.io/integrations/calendar/) entity. You can view the program schedule in the UI, or trigger other automations
+based on the irrigation start or end time.
+
 ## Number
 
 The Rain Delay Number Entity lets you set and view  the number of days, if any, the automatic irrigation schedule has been delayed.