Add output button documentation (#1846)

Co-authored-by: Jesse Hills <3060199+jesserockz@users.noreply.github.com>

components/button/output.rst

@@ -0,0 +1,49 @@
+Generic Output Button
+=====================
+
+.. seo::
+    :description: Instructions for setting up generic output buttons in ESPHome that control an output component.
+    :image: upload.svg
+
+The ``output`` button platform allows you to use any output component as a button. This can for example be used to
+momentarily set a GPIO pin using a button.
+
+.. figure:: images/generic-ui.png
+    :align: center
+    :width: 80.0%
+
+.. code-block:: yaml
+
+    # Example configuration entry
+    output:
+      - platform: gpio
+        pin: 25
+        id: output1
+
+    button:
+      - platform: output
+        name: "Generic Output"
+        output: output1
+        duration: 500ms
+
+Configuration variables:
+------------------------
+
+- **name** (**Required**, string): The name for the button.
+- **id** (*Optional*, :ref:`config-id`): Manually specify the ID used for code generation.
+- **output** (**Required**, :ref:`config-id`): The ID of the output component to use.
+- **duration** (**Required**, :ref:`config-time`): How long the output should be set when the button is pressed.
+- All other options from :ref:`Button <config-button>`.
+
+.. note::
+
+    When used with a :doc:`/components/output/gpio`, the pin will be low by default and pulled high when the button is
+    pressed. To invert this behaviour and have the pin pulled low when the button is pressed, set the `inverted` option
+    in the :ref:`config-pin_schema`.
+
+See Also
+--------
+
+- :doc:`/components/output/index`
+- :apiref:`output/button/output_button.h`
+- :ghedit:`Edit`

index.rst

@@ -484,6 +484,7 @@ Button Components
 
     Button Core, components/button/index, folder-open.svg
     Template Button, components/button/template, description.svg
+    Generic Output Button, components/button/output, upload.svg
     Restart Button, components/button/restart, restart.svg
     Wake-on-LAN, components/button/wake_on_lan, power_settings.svg