Add to README that only Qt 4.8 is supported.
Add to README that only Qt 4.8 is supported.

Change-Id: I236ebc67895ac4159672fc12cd912c8ff17407e4
Reviewed-by: Tim Jenssen <6a21f175c697b4129e1bafb6e9b52078bb1a6738@digia.com>

olear/qtifw,olear/qtifw,olear/qtifw,olear/qtifw