doc: Add AppVeyor master branch build status badge
doc: Add AppVeyor master branch build status badge

schuhschuh/MIRTK,schuhschuh/MIRTK,BioMedIA/MIRTK,BioMedIA/MIRTK,schuhschuh/MIRTK,BioMedIA/MIRTK,schuhschuh/MIRTK,BioMedIA/MIRTK