Compute shader chapter documentation not properly updated to timeline semaphores

The compute shader chapter code been updated to use Timeline semaphores. The documentation though hasn't been properly updated and still uses separate fences, e.g.:

```
We then use these to synchronize the compute buffer submission with the graphics submission:

[,c++]
----
{
// Compute submission
while ( vk::Result::eTimeout == device->waitForFences(**computeInFlightFences[frameIndex], vk::True, UINT64_MAX) )
;

updateUniformBuffer(frameIndex);
device->resetFences( **computeInFlightFences[frameIndex] );
computeCommandBuffers[frameIndex]->reset();
recordComputeCommandBuffer();

const vk::SubmitInfo submitInfo({}, {}, {**computeCommandBuffers[frameIndex]}, { **computeFinishedSemaphores[frameIndex]});
computeQueue->submit(submitInfo, **computeInFlightFences[frameIndex]);
}
{
// Graphics submission
while ( vk::Result::eTimeout == device->waitForFences(**inFlightFences[frameIndex], vk::True, UINT64_MAX))
...

device->resetFences( **inFlightFences[frameIndex] );
commandBuffers[frameIndex]->reset();
recordCommandBuffer(imageIndex);

vk::Semaphore waitSemaphores[] = {**presentCompleteSemaphore[frameIndex], **computeFinishedSemaphores[frameIndex]};
vk::PipelineStageFlags waitDestinationStageMask[] = { vk::PipelineStageFlagBits::eVertexInput, vk::PipelineStageFlagBits::eColorAttachmentOutput };
const vk::SubmitInfo submitInfo( waitSemaphores, waitDestinationStageMask, {**commandBuffers[frameIndex]}, {**renderFinishedSemaphore[frameIndex]} );
graphicsQueue->submit(submitInfo, **inFlightFences[frameIndex]);
----
```