added documentation for the text-decoration-control component

packages/block-editor/src/components/text-decoration-control/README.md

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+# TextDecorationControl
+
+![TextDecorationControl Element in Inspector Control](https://raw.githubusercontent.com/WordPress/gutenberg/HEAD/docs/assets/text-decoration-component.png?raw=true)
+
+## Table of Contents
+
+1. [Usage](#usage)
+3. [Properties](#props)
+
+## Usage
+
+```jsx
+import { TextDecorationControl } from '@wordpress/block-editor';
+```
+
+Then, you can use the component in your block editor UI:
+
+```jsx
+<TextDecorationControl
+  value={textDecorationValue}
+  onChange={(newValue) => setAttributes({ textDecoration: newValue })}
+/>
+```
+
+### Props
+
+### `value`
+
+-   **Type:** `String`
+-   **Default:** `none`
+-   **Options:** `none`, `underline`, `line-through`
+
+The current value of the Text Decoration setting. You may only choose from the `Options` listed above.
+
+### `onChange`
+
+-   **Type:** `Function`
+
+A callback function invoked when the Text Decoration value is changed via an interaction with any of the buttons. Called with the Text Decoration value (`none`, `underline`, `line-through`) as the only argument.