Android: document the supported clipboard mimetypes

Fixes: QTBUG-82477
Pick-to: 5.15 6.2 6.3 6.4
Change-Id: I31a48acbf5cadc18dfe1fe9a54243b710f4f280c
Reviewed-by: Andy Shaw <andy.shaw@qt.io>

src/gui/kernel/qclipboard.cpp

@@ -103,6 +103,10 @@ using namespace Qt::StringLiterals;
 
     \endlist
 
+    \section1 Notes for Android Users
+
+    On Android only these mime types are supported: text/plain, text/html, and text/uri-list.
+
     \sa QGuiApplication
 */