Drop references to VIGRA build from README
Drop references to VIGRA build from README

nanshe-org/rank_filter,jakirkham/rank_filter,nanshe-org/rank_filter,DudLab/rank_filter,DudLab/rank_filter,DudLab/rank_filter,jakirkham/rank_filter,nanshe-org/rank_filter,jakirkham/rank_filter