Add the widget reference for Checkbox

docs/widgets/checkbox.md

@@ -0,0 +1,59 @@
+# Checkbox
+
+A simple checkbox width which stores a boolean value.
+
+- [x] Focusable
+- [ ] Container
+
+## Example
+
+The example below shows switches in various states.
+
+=== "Output"
+
+    ```{.textual path="docs/examples/widgets/checkbox.py"}
+    ```
+
+=== "checkbox.py"
+
+    ```python
+    --8<-- "docs/examples/widgets/checkbox.py"
+    ```
+
+=== "checkbox.css"
+
+    ```sass
+    --8<-- "docs/examples/widgets/checkbox.css"
+    ```
+
+## Reactive Attributes
+
+| Name    | Type   | Default | Description                |
+|---------|--------|---------|----------------------------|
+| `value` | `bool` | `False` | The value of the checkbox. |
+
+## Bindings
+
+The checkbox widget defines directly the following bindings:
+
+::: textual.widgets._toggle_button.ToggleButton.BINDINGS
+    options:
+      show_root_heading: false
+      show_root_toc_entry: false
+
+## Component Classes
+
+The checkbox widget provides the following component classes:
+
+::: textual.widgets._toggle_button.ToggleButton.COMPONENT_CLASSES
+    options:
+      show_root_heading: false
+      show_root_toc_entry: false
+
+## Messages
+
+### ::: textual.widgets.Checkbox.Changed
+
+## See Also
+
+- [Checkbox](../api/checkbox.md) code reference