Update MVS.rst

Not sure why there are these two lines:
  $ cmvs Dataset/outReconstruction/SfM_Output/PMVS/ [MaxImageCountByCluster=100]
  $ cmvs Dataset/outReconstruction/SfM_Output/PMVS/ 30

Updated line specifies max images per cluster 100, with 5 CPUs
  $ cmvs Dataset/outReconstruction/SfM_Output/PMVS/ 100 6