title: Confused with some Vulkan concept
body: <p>i have some few questions about Vulkan concepts.</p>
  <p><strong>1. vkCmdBindDescriptorSets arguments</strong></p>
  <pre><code>// Provided by VK_VERSION_1_0
  there is prototype:
  void vkCmdBindDescriptorSets(
      VkCommandBuffer                             commandBuffer,
      VkPipelineBindPoint                         pipelineBindPoint,
      VkPipelineLayout                            layout,
      uint32_t                                    firstSet,
      uint32_t                                    descriptorSetCount,
      const VkDescriptorSet*                      pDescriptorSets,
      uint32_t                                    dynamicOffsetCount,
      const uint32_t*                             pDynamicOffsets);
  </code></pre>
  <p>i want to know the usage of descriptorSetCount and pDescriporSets, pipeline use only one VkDescriptorSet in a drawcall,but provide multiply same layout VkDescriptorSet means what?</p>
  <p><strong>2. glsl uniform layout</strong></p>
  <pre><code>layout(set=0,binding =0) uniform UniformBufferObject
  {
      mat4 view;
      mat4 projection;
      vec3 position_camera;
  }ubo;
  </code></pre>
  <p>what does set means?</p>