fix bitrotted reference to sample.txt in README
fix bitrotted reference to sample.txt in README

nzjrs/pinpoint,robclark/pinpoint,potofcoffee/pinpoint,robclark/pinpoint,danigm/pinpoint,nekohayo/pinpoint,bpeel/pinpoint,danigm/pinpoint,potofcoffee/pinpoint,tyll/pinpoint,nekohayo/pinpoint,nzjrs/pinpoint,michaelgwood/pinpoint,tyll/pinpoint,GNOME/pinpoint,michaelgwood/pinpoint,bpeel/pinpoint,GNOME/pinpoint,robclark/pinpoint