Add thrust tutorial in the GPU main page documentation.

doc/tutorials/gpu/gpu-thrust-interop/gpu_thrust_interop.markdown

-Using a cv::cuda::GpuMat with thrust
+Using a cv::cuda::GpuMat with thrust {#tutorial_gpu_thrust_interop}
 ===========================================
 
 Goal

doc/tutorials/gpu/table_of_content_gpu.markdown

@@ -13,3 +13,10 @@ run the OpenCV algorithms.
     This will give a good grasp on how to approach coding on the GPU module, once you already know
     how to handle the other modules. As a test case it will port the similarity methods from the
     tutorial @ref tutorial_video_input_psnr_ssim to the GPU.
+
+-   @subpage tutorial_gpu_thrust_interop
+
+    *Compatibility:* \>= OpenCV 3.0
+
+    This tutorial will show you how to wrap a GpuMat into a thrust iterator in order to be able to
+    use the functions in the thrust library.