chore: Update README to note that 0.2.12 is the last version to support Python 2
chore: Update README to note that 0.2.12 is the last version to support Python 2

Signed-off-by: Kai Blin <ad3597797f6179d503c382b2627cc19939309418@biosustain.dtu.dk>

kblin/ncbi-genome-download,kblin/ncbi-genome-download