Document state of Dozen Vulkan support in features.txt for MesaMatrix site..
Dozen is merged and will be in Mesa 22.1 stable.. there are patches which seem to bring support for Vulkan1.1 soon.. I would desire to track Vulkan Dozen support on MesaMatrix.. so I opened https://github.com/MightyCreak/mesamatrix/issues/235 and seems it tracks Mesa features.txt document (in this case needed for Dozen)..