Update README before changing repo name to GATK
Update README before changing repo name to GATK

Added links to current GATK website + repos to stave off possible confusion as mentioned in #945

magicDGS/gatk,ksthesis/gatk,ksthesis/gatk,magicDGS/gatk,frank-y-liu/gatk,frank-y-liu/gatk,magicDGS/gatk,ksthesis/gatk,frank-y-liu/gatk,broadinstitute/hellbender,magicDGS/gatk,ksthesis/gatk,broadinstitute/hellbender,broadinstitute/hellbender,magicDGS/gatk,ksthesis/gatk,broadinstitute/hellbender,broadinstitute/gatk-dataflow,frank-y-liu/gatk,broadinstitute/gatk-dataflow,broadinstitute/hellbender,broadinstitute/hellbender,frank-y-liu/gatk,frank-y-liu/gatk,ksthesis/gatk,magicDGS/gatk