Add readme to output directory

[snayfach]

I find it really nice when there's a readme included in the output folder that describes the contents. You've named the files well, but can be nice to have them explained in a file

$ ls

check_fna_paths.list core_snps.vcf kmer_db.bin logfile reference.fna tag_msa.fna temp coords.tsv gt_results kmer_prof.tsv nr_kmer_set.tsv selected_kmers.tsv tag_paths.list

[zjshi]

I like this idea. Instead of adding an readme file, I made the program to print it instead.