Update README.md

Update readme to reflect new class name, pod name, pod version, and update installation procedure.

Please review the changes, I'm not 100% sure everything is correct.

I also made an updated version of the image at https://dl.dropboxusercontent.com/u/18386288/DZWebBrowser.png. Although don't link directly to my dropbox, as I will probably not keep the image up indefinitely.

![DZNWebViewController](https://dl.dropboxusercontent.com/u/18386288/DZWebBrowser.png)