Fixed minor typos in README.
Fixed minor typos in README.

heuermh/adam,bigdatagenomics/adam,heuermh/adam,bigdatagenomics/adam,laserson/adam,bigdatagenomics/adam,bigdatagenomics/adam,laserson/adam,heuermh/adam,laserson/adam,laserson/adam,heuermh/adam