Usage:
./sourmash compute --scaled 5000 data/GCF_000005845.2_ASM584v2_genomic.fna.gz -f
python e7d910326792554e1fbf826fe12da83f/subscaled.py GCF_000005845.2_ASM584v2_genomic.fna.gz.sig foo.sig 10000
and now foo.sig
will contain the newly subscaled signature.