docs for new switch binary sensor (#4465)

Co-authored-by: Samuel Sieb <samuel@sieb.net>
Co-authored-by: Jesse Hills <3060199+jesserockz@users.noreply.github.com>

components/binary_sensor/switch.rst

@@ -0,0 +1,36 @@
+.. _switch-binary-sensor:
+
+Switch Binary Sensor
+====================
+
+.. seo::
+    :description: Instructions for setting up switch binary sensors with ESPHome.
+
+The Switch Binary Sensor platform allows you to view the state of any switch component as a
+read-only binary sensor.
+
+.. code-block:: yaml
+
+    # Example configuration entry
+    binary_sensor:
+      - platform: switch
+        name: "Output state"
+        source_id: relay1
+
+    switch:
+      - platform: gpio
+        id: relay1
+        pin: GPIOXX
+
+Configuration variables:
+------------------------
+
+- **source_id** (**Required**, :ref:`config-id`): The source switch to observe.
+- All other options from :ref:`Binary Sensor <config-binary_sensor>`.
+
+See Also
+--------
+
+- :doc:`/components/binary_sensor/index`
+- :apiref:`switch/binary_sensor/switch_binary_sensor.h`
+- :ghedit:`Edit`

index.rst

@@ -637,6 +637,7 @@ Core
     GPIO, components/binary_sensor/gpio, gpio.svg
     Home Assistant, components/binary_sensor/homeassistant, home-assistant.svg, dark-invert
     Status, components/binary_sensor/status, server-network.svg, dark-invert
+    Switch, components/binary_sensor/switch, electric-switch.svg, dark-invert
 
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