docs(y-indexeddb): add README.md (#1886)

packages/y-indexeddb/README.md

@@ -0,0 +1,18 @@
+# @toeverything/y-indexeddb
+
+> This package haven't been published yet.
+
+## Usage
+
+```ts
+import { createIndexedDBProvider } from '@toeverything/y-indexeddb';
+import * as Y from 'yjs';
+const yDoc = new Y.Doc();
+
+const provider = createIndexedDBProvider('docName', yDoc);
+provider.connect();
+await provider.whenSynced.then(() => {
+  console.log('synced');
+  provider.disconnect();
+});
+```