New js modules documentation added (#3736)

* New js modules documentation added
* Documentation: Spelling and formatting

Co-authored-by: ElectronicsInFocus <rnadyrshin@gmail.com>
Co-authored-by: あく <alleteam@gmail.com>

documentation/js/js_submenu.md

@@ -0,0 +1,48 @@
+# js_submenu {#js_submenu}
+
+# Submenu module
+```js
+let submenu = require("submenu");
+```
+# Methods
+
+## setHeader
+Set the submenu header text.
+
+### Parameters
+- header (string): The submenu header text
+
+### Example
+```js
+submenu.setHeader("Select an option:");
+```
+
+## addItem
+Add a new submenu item.
+
+### Parameters
+- label (string): The submenu item label text
+- id (number): The submenu item ID, must be a Uint32 number
+
+### Example
+```js
+submenu.addItem("Option 1", 1);
+submenu.addItem("Option 2", 2);
+submenu.addItem("Option 3", 3);
+```
+
+## show
+Show a submenu that was previously configured using `setHeader()` and `addItem()` methods.
+
+### Returns
+The ID of the submenu item that was selected, or `undefined` if the BACK button was pressed.
+
+### Example
+```js
+let selected = submenu.show();
+if (selected === undefined) {
+    // if BACK button was pressed
+} else if (selected === 1) {
+    // if item with ID 1 was selected
+}
+```