Clarify documentation for QImageCapture's 'ready' property.

Unlike what was described in the documentation, it's not permissible to
call capture() while 'ready' or isReadyForCapture() is false. All
backends emit an error in that case.
Updated the documentation to reflect that behavior.

Change-Id: Icb326e65376b65eadd4c68b67e0ee30beddf1a04
Reviewed-by: Venugopal Shivashankar <venugopal.shivashankar@digia.com>
Reviewed-by: Christian Stromme <christian.stromme@theqtcompany.com>

src/multimedia/camera/qcameraimagecapture.cpp

@@ -488,11 +488,8 @@ void QCameraImageCapture::setCaptureDestination(QCameraImageCapture::CaptureDest
   \property QCameraImageCapture::readyForCapture
   \brief whether the service is ready to capture a an image immediately.
 
-   It's permissible to call capture() while the camera status is QCamera::ActiveStatus
-   regardless of isReadyForCapture property value.
-   If camera is not ready to capture image immediately,
-   the capture request is queued with all the related camera settings
-   to be executed as soon as possible.
+  Calling capture() while \e readyForCapture is \c false is not permitted and
+  results in an error.
 */
 
 bool QCameraImageCapture::isReadyForCapture() const
@@ -528,6 +525,8 @@ bool QCameraImageCapture::isReadyForCapture() const
 
     QCameraImageCapture::capture returns the capture Id parameter, used with
     imageExposed(), imageCaptured() and imageSaved() signals.
+
+    \sa isReadyForCapture()
 */
 int QCameraImageCapture::capture(const QString &file)
 {