update readme for storage

<a href='#crh-start'></a><a href='#crh-data-%7B%7D'></a>
<a href='https://www.codereviewhub.com/'><img src='http://www.codereviewhub.com/site/github-bar.png' height=40></a>
<a href='https://www.codereviewhub.com/AzureAD/azure-activedirectory-library-for-js/pull/63?approve=1'><img src='http://www.codereviewhub.com/site/github-approve.png' height=26></a>&nbsp;<a href='https://github.com/AzureAD/azure-activedirectory-library-for-js/pull/63'><img src='http://www.codereviewhub.com/site/github-refresh.png' height=26></a>
<a href='#crh-end'></a>