Document Footer widget

docs/widgets/footer.md

@@ -1 +1,41 @@
 # Footer
+
+## Description
+
+A simple footer widget which is docked to the bottom of its parent container. Displays
+available keybindings for the currently focused widget.
+
+## Example
+
+The example below shows an app with a single keybinding that contains only a `Footer`
+widget. Notice how the `Footer` automatically displays the keybind.
+
+=== "Output"
+
+    ```{.textual path="docs/examples/widgets/footer.py"}
+    ```
+
+=== "button.py"
+
+    ```python
+    --8<-- "docs/examples/widgets/footer.py"
+    ```
+
+## Reactive Attributes
+
+| Name            | Type  | Default | Description                                                                                               |
+|-----------------|-------|---------|-----------------------------------------------------------------------------------------------------------|
+| `highlight_key` | `str` | `None`  | Stores the currently highlighted key. This is typically the key the cursor is hovered over in the footer. |
+
+## Messages
+
+This widget sends no messages.
+
+## Additional Notes
+
+* You can prevent keybindings from appearing in the footer by setting the `show` argument of the `Binding` to `False`.
+* You can customize the text that appears for the key itself in the footer using the `key_display` argument of `Binding`.
+
+## See Also
+
+* [Footer](../reference/footer.md) code reference