Better readme for the edit-navigation package (#23018)

* Better readme for the edit-navigation package

* Improve tagline

packages/edit-navigation/README.md

@@ -1,5 +1,67 @@
-- Package name
-- Package description
-- Installation details
-- Usage example
-- `Code is Poetry` logo (`<br/><br/><p align="center"><img src="https://s.w.org/style/images/codeispoetry.png?1" alt="Code is Poetry." /></p>`)
+# Edit navigation
+
+Edit Navigation page module for WordPress - a Gutenberg-based UI for editing navigation menus.
+
+> This package is meant to be used only with WordPress core. Feel free to use it in your own project but please keep in mind that it might never get fully documented.
+
+## Usage
+
+```js
+/**
+ * WordPress dependencies
+ */
+import { initialize } from '@wordpress/edit-navigation';
+
+/**
+ * Internal dependencies
+ */
+import blockEditorSettings from './block-editor-settings';
+
+initialize( '#navigation-editor-root', blockEditorSettings );
+
+```
+
+## Hooks
+
+`useMenuItems` and `useNavigationBlock` hooks are the central part of this package. They bridge the gap between the API and the block editor interface:
+
+```js
+const menuId = 1;
+const query = useMemo( () => ( { menus: menuId, per_page: -1 } ), [
+    menuId,
+] );
+// Data manipulation:
+const {
+    menuItems,
+    eventuallySaveMenuItems,
+    createMissingMenuItems,
+} = useMenuItems( query );
+
+// Working state:
+const { blocks, setBlocks, menuItemsRef } = useNavigationBlocks(
+    menuItems
+);
+
+return (
+    <BlockEditorProvider
+        value={ blocks }
+        onInput={ ( updatedBlocks ) => setBlocks( updatedBlocks ) }
+        onChange={ ( updatedBlocks ) => {
+            createMissingMenuItems( updatedBlocks, menuItemsRef );
+            setBlocks( updatedBlocks );
+        } }
+        settings={ blockEditorSettings }
+    >
+        <NavigationStructureArea blocks={ blocks } initialOpen />
+        <BlockEditorArea
+            menuId={ menuId }
+            saveBlocks={ () => eventuallySaveMenuItems( blocks, menuItemsRef ) }
+            onDeleteMenu={ () => { /* ... */ } }
+        />
+    </BlockEditorProvider>
+);
+```
+
+_This package assumes that your code will run in an **ES2015+** environment. If you're using an environment that has limited or no support for ES2015+ such as lower versions of IE then using [core-js](https://github.com/zloirock/core-js) or [@babel/polyfill](https://babeljs.io/docs/en/next/babel-polyfill) will add support for these methods. Learn more about it in [Babel docs](https://babeljs.io/docs/en/next/caveats)._
+
+<br/><br/><p align="center"><img src="https://s.w.org/style/images/codeispoetry.png?1" alt="Code is Poetry." /></p>