QtIFW

Doc: add the XML requirement for escaping <

One must use the character reference "&lt;" to escape
the left angle bracket within XML elements.

Change-Id: I69d3683b3a3b1e9f3e62cb6199e554d13de1f58f
Reviewed-by: Jarek Kobus <jaroslaw.kobus@theqtcompany.com>
Reviewed-by: Christoph Vogtländer <c.vogtlaender@sigma-surface-science.com>