CLI cat: clarify BAM and header things in --help
CLI cat: clarify BAM and header things in --help

ryan-williams/Hadoop-BAM,fnothaft/Hadoop-BAM,HadoopGenomics/Hadoop-BAM,cmnbroad/Hadoop-BAM,fnothaft/Hadoop-BAM,cmnbroad/Hadoop-BAM,tkrishp/Hadoop-BAM,fnothaft/Hadoop-BAM,tomwhite/Hadoop-BAM,HadoopGenomics/Hadoop-BAM,HadoopGenomics/Hadoop-BAM,ryan-williams/Hadoop-BAM