add submenu docs

docs/source/conf.py

@@ -65,8 +65,8 @@
     "**": ["sidebar_main_nav_links.html", "sidebar_toc.html"]
 }
 html_permalinks_icon = Icons.permalinks_icon
-html_logo = "../_static/lcdmenu.svg"
-html_favicon = "../_static/lcdmenu.svg"
+html_logo = "../assets/lcdmenu.svg"
+html_favicon = "../assets/lcdmenu.svg"
 html_theme_options = {
     'show_scrolltop': True,
     'show_prev_next': True,

docs/source/overview/deep-dive/submenu.rst

@@ -0,0 +1,36 @@
+Sub-menu item
+-------------
+
+The sub-menu item is a menu item that opens a new menu screen when selected.
+It is used to create a hierarchical menu structure with multiple levels of navigation.
+
+This can be useful for organizing menu items into categories or sub-menus, making it easier for users to navigate through the menu system.
+
+A sub-menu item can be created using the following syntax:
+
+You first need to define the sub-menu screen with the desired menu items:
+
+.. code-block:: cpp
+
+    MENU_SCREEN(subMenuScreen, subMenuItems,
+        ITEM_BASIC("Sub-item 1"),
+        ITEM_BASIC("Sub-item 2"),
+        ITEM_BASIC("Sub-item 3"),
+        ITEM_BASIC("Sub-item 4"));
+
+Then you can create a sub-menu item entry that links to the sub-menu screen in the parent menu:
+
+.. code-block:: cpp
+
+    // ... More menu items
+    ITEM_SUBMENU("Sub-menu 1", subMenuScreen)
+    // ... More menu items
+
+When the ``Sub-menu 1`` menu item is selected, the sub-menu screen will be displayed, showing the list of sub-items.
+
+.. image:: images/item-submenu.gif
+    :alt: Example of a sub-menu item
+
+You can create multiple levels of sub-menus by nesting sub-menu items within other sub-menu screens.
+
+Find more information about the sub-menu item in the :doc:`API reference </reference/api/ItemSubMenu>`.