Update README with new numbers after pre-filtering the junction probes,
which lowers the numbers by 1856, i.e. the number of junction probes
out of the total 5587 that had previously been mapped by bwa. Also
update the description to accurately specify that the reads were
filtered by quality score and not a perfect match (reads with score of
37 can still have mismatches if it is very unlikely they map anywhere
else in the genome).