Update Checkbox.ipynb to indicate both Toggle and Switch are intercha…

…ngeable with Checbox. (#7738)

Textual improvements to clarify all 3 widgets are interchangeable, and adds links to the 2 docs for the other widgets that are interchangeable. See #7737

No entirely sure if the added links are structured correctly, so that they will be converted to correct links when the webpage is generated from the Notebook.

See issue #7737 for request for further explanation on this.

examples/reference/widgets/Checkbox.ipynb

@@ -14,7 +14,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "The ``Checkbox`` widget allows toggling a single condition between ``True``/``False`` states by ticking a checkbox. This widget is interchangeable with the ``Toggle`` widget.\n",
+    "The ``Checkbox`` widget allows toggling a single condition between ``True``/``False`` states by ticking a checkbox. The `Checkbox` widget allows toggling a single condition between `True`/`False` states by ticking a checkbox. The [``Checkbox``](Checkbox.ipynb), [``Toggle``](Toggle.ipynb), and [``Switch``](Switch.ipynb) widgets are interchangeable.\n",
     "\n",
     "Discover more on using widgets to add interactivity to your applications in the [how-to guides on interactivity](../../how_to/interactivity/index.md). Alternatively, learn [how to set up callbacks and (JS-)links between parameters](../../how_to/links/index.md) or [how to use them as part of declarative UIs with Param](../../how_to/param/index.md).\n",
     "\n",