Doc: Added information about the tagged desktop examples
Doc: Added information about the tagged desktop examples

This change informs developers about listing the examples that are
tested for Android so that they don't annoy themselves by trying to
run examples that don't work.

Task-number: QTBUG-30173
Change-Id: I0c422ebf265247c96e63c22fc4a76f28eb37a7d3
Reviewed-by: Topi Reiniö <92400b03a70fe3119347f89b476f73d34ae93598@digia.com>
Reviewed-by: Jerome Pasion <c10995d24f6b454503389e8d00d837aef038985d@digia.com>

kobolabs/qtdoc,kobolabs/qtdoc,kobolabs/qtdoc,kobolabs/qtdoc