Fix versioning in qdocconf files

Change-Id: I162ea62fe63cb44c7476727a4952ce95a1f543ab
Reviewed-by: Jędrzej Nowacki <jedrzej.nowacki@digia.com>
Update install instructions

Task-number: QTBUG-35119

Change-Id: If51629d60694ced7d192a77da72c4cf572094137
Reviewed-by: Jędrzej Nowacki <jedrzej.nowacki@digia.com>