Update docs

docs/designers-developers/developers/slotfills/main-dashboard-button.md

@@ -1,9 +1,12 @@
 # MainDashboardButton
 
-This slot allows replacing the default main dashboard button that's used for closing
-the editor in fullscreen mode.
+This slot allows replacing the default main dashboard button in the post editor 
+that's used for closing the editor in fullscreen mode. In the site editor this slot
+refers to the "back to dashboard" button in the navigation sidebar.
 
-## Example
+## Examples
+
+Basic usage:
 
 ```js
 import { registerPlugin } from '@wordpress/plugins';
@@ -22,8 +25,8 @@ registerPlugin( 'main-dashboard-button-test', {
 } );
 ```
 
-If your goal is just to replace the icon of the existing button, that can be achieved
-in the following way:
+If your goal is just to replace the icon of the existing button in
+the post editor, that can be achieved in the following way:
 
 ```js
 import { registerPlugin } from '@wordpress/plugins';
@@ -46,3 +49,29 @@ registerPlugin( 'main-dashboard-button-icon-test', {
 	render: MainDashboardButtonIconTest,
 } );
 ```
+
+Site editor example:
+
+```js
+import { registerPlugin } from '@wordpress/plugins';
+import {
+	__experimentalMainDashboardButton as MainDashboardButton,
+} from '@wordpress/interface';
+import {
+	__experimentalNavigationBackButton as NavigationBackButton,
+} from '@wordpress/components';
+
+const MainDashboardButtonIconTest = () => (
+    <MainDashboardButton>
+        <NavigationBackButton
+            backButtonLabel={ __( 'Back to dashboard' ) }
+            className="edit-site-navigation-panel__back-to-dashboard"
+            href="index.php"
+        />
+    </MainDashboardButton>
+);
+
+registerPlugin( 'main-dashboard-button-icon-test', {
+	render: MainDashboardButtonIconTest,
+} );
+```