Added the script to plot plink/seq brca1 ibs matrix.

Not anything to do for this PR, but just a general comment:

It would be interesting to compare the individuals declared similar here to those that appear to be similar according to the PCA results for BRCA1 https://github.com/googlegenomics/codelabs/blob/master/R/1000Genomes-BRCA1-analysis/AllModalitiesDemo.md#zooming-in