Doc: Added information about WebSockets in connectivity article.

-better integration and visibility to Qt WebSockets.

Task-number: QTBUG-40901
Change-Id: I1791b2ccb686e08e12c2eaa36a4d0a92debd21bc
Reviewed-by: Kurt Pattyn <pattyn.kurt@gmail.com>
Reviewed-by: Venugopal Shivashankar <venugopal.shivashankar@digia.com>
Reviewed-by: Leena Miettinen <riitta-leena.miettinen@digia.com>