message: Doc warnings about experimental UMatUsageFlags
diff: @@ -458,7 +458,16 @@ CV_EXPORTS InputOutputArray noArray();
  /////////////////////////////////// MatAllocator //////////////////////////////////////
  -//! Usage flags for allocator
  +/** @brief Usage flags for allocator
  +
  + @warning All flags except `USAGE_DEFAULT` are experimental.
  +
  + @warning For the OpenCL allocator, `USAGE_ALLOCATE_SHARED_MEMORY` depends on
  + OpenCV's optional, experimental integration with OpenCL SVM. To enable this
  + integration, build OpenCV using the `WITH_OPENCL_SVM=ON` CMake option and, at
  + runtime, call `cv::ocl::Context::getDefault().setUseSVM(true);` or similar
  + code. Note that SVM is incompatible with OpenCL 1.x.
  +*/
  enum UMatUsageFlags
  {
  USAGE_DEFAULT = 0,
  