Improve description of QRhiTextureSubresourceUploadDescription::setImage

The format of QImage is not considered upon texture loading,
it should be documented.

Pick-to: 6.6 6.5
Change-Id: I795c8a82a71ecdba5407f7e4ce940f7d538ff924
Reviewed-by: Jøger Hansegård <joger.hansegard@qt.io>
Reviewed-by: Artem Dyomin <artem.dyomin@qt.io>
(cherry picked from commit f2957e463362b307c1cc736365c4640c9befbdd0)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

src/gui/rhi/qrhi.cpp

@@ -2750,6 +2750,7 @@ QRhiTextureSubresourceUploadDescription::QRhiTextureSubresourceUploadDescription
     \fn void QRhiTextureSubresourceUploadDescription::setImage(const QImage &image)
 
     Sets \a image.
+    Upon textures loading, the image data will be read as is, with no formats conversions.
 
     \note image() and data() cannot be both set at the same time.
  */