Add template for widget reference.

docs/widgets/_template.md

@@ -0,0 +1,64 @@
+# Widget
+
+Widget description.
+
+- [ ] Focusable
+- [ ] Container
+
+
+## Example
+
+Example app showing the widget:
+
+=== "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
+
+
+## Bindings
+
+The WIDGET widget defines directly the following bindings:
+
+::: textual.widgets.WIDGET.BINDINGS
+    options:
+      show_root_heading: false
+      show_root_toc_entry: false
+
+
+## Component classes
+
+The WIDGET widget provides the following component classes:
+
+::: textual.widget.WIDGET.COMPONENT_CLASSES
+    options:
+      show_root_heading: false
+      show_root_toc_entry: false
+
+
+## Additional notes
+
+- Did you know this?
+- Another pro tip.
+
+
+## See also
+
+- [WIDGET](../api/WIDGET.md) code reference.
+- Another related API.
+- Something else useful.