Explicitly explain the `--target-genomes` call and how it must be tupleized.
Explicitly explain the `--target-genomes` call and how it must be tupleized.

For issue #44.

ComparativeGenomicsToolkit/Comparative-Annotation-Toolkit,ucsc-mus-strain-cactus/Comparative-Annotation-Toolkit,ComparativeGenomicsToolkit/Comparative-Annotation-Toolkit