Add README for WritingModeControl component

packages/block-editor/src/components/writing-mode-control/README.md

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+# WritingModeControl
+
+WritingModeControl is a React component that renders a UI that allows users to select text orientation (writing mode).
+The component provides a toggle group interface that allows users to switch between horizontal and vertical text orientations, with automatic RTL (Right-to-Left) support.
+
+## Usage
+
+```jsx
+import { WritingModeControl } from '@wordpress/block-editor';
+import { useState } from '@wordpress/element';
+
+const MyWritingModeControl = () => {
+    const [ writingMode, setWritingMode ] = useState();
+
+    return (
+        <WritingModeControl
+            value={ writingMode }
+            onChange={ ( newWritingMode ) => {
+                setWritingMode( newWritingMode );
+            } }
+        />
+    );
+};
+```
+
+## Props
+
+The component accepts the following props:
+
+### onChange
+
+A function that handles change in the writing mode selection.
+
+- Type: `function`
+- Required: Yes
+
+### value
+
+The current writing mode value. Can be one of:
+- `'horizontal-tb'` - Horizontal top-to-bottom text
+- `'vertical-rl'` - Vertical right-to-left text (for LTR languages)
+- `'vertical-lr'` - Vertical left-to-right text (for RTL languages)
+
+- Type: `string`
+- Required: No
+- Default: `undefined`
+
+### className
+
+Additional class name to add to the control.
+
+- Type: `string`
+- Required: No