added brush to index nb
added brush to index nb

dmadeka/bqplot,bloomberg/bqplot,SylvainCorlay/bqplot,dmadeka/bqplot,bloomberg/bqplot,SylvainCorlay/bqplot,ChakriCherukuri/bqplot,SylvainCorlay/bqplot,ChakriCherukuri/bqplot,ChakriCherukuri/bqplot,bloomberg/bqplot