Create basic react-native integration guide (#770)

Author: pradel

website/docs/cookbook/react-native.md

@@ -0,0 +1,21 @@
+---
+id: react-native
+title: react-native
+sidebar_label: react-native
+---
+
+By default accounts-js use the `localStorage` api to store the tokens.
+
+Since react-native does not have `localStorage`, we can use the [React Native Async Storage](https://github.com/react-native-community/async-storage).
+
+To setup the client to use the AsyncStorage api you need to apply the following configuration:
+
+```javascript
+import AsyncStorage from '@react-native-community/async-storage';
+import { AccountsClient } from '@accounts/client';
+
+const accounts = new AccountsClient({
+  // We tell the accounts-js client to use AsyncStorage to store the tokens
+  tokenStorage: AsyncStorage,
+});
+```

website/sidebars.js

@@ -17,6 +17,7 @@ module.exports = {
       'strategies/oauth',
       'strategies/twitter',
     ],
+    Cookbook: ['cookbook/react-native'],
   },
   api: {
     'Api Docs': [