Update readme to include beta reference (#391)

Author: frederikprijck

README.md

@@ -2,6 +2,8 @@
 
 A library for integrating [Auth0](https://auth0.com) into an Angular application.
 
+> :warning: Please be aware that v2 is currently in [**Beta**](https://auth0.com/docs/troubleshoot/product-lifecycle/product-release-stages). Whilst we encourage you to test the update within your applications, we do no recommend using this version in production yet. Please follow the [migration guide](./MIGRATION_GUIDE.md) when updating your application.
+
 ![Release](https://img.shields.io/npm/v/@auth0/auth0-angular)
 [![Codecov](https://img.shields.io/codecov/c/github/auth0/auth0-angular)](https://codecov.io/gh/auth0/auth0-angular)
 ![Downloads](https://img.shields.io/npm/dw/@auth0/auth0-angular)
@@ -29,13 +31,13 @@ This project only supports the [actively supported versions of Angular as stated
 Using npm:
 
 ```sh
-npm install @auth0/auth0-angular
+npm install @auth0/auth0-angular@beta
 ```
 
 We also have `ng-add` support, so the library can also be installed using the Angular CLI:
 
 ```sh
-ng add @auth0/auth0-angular
+ng add @auth0/auth0-angular@beta
 ```
 
 ### Configure Auth0