Documentation improvement: Describe output of validate_demultiplexed_fasta.py

[AmandaBirmingham]

I recently used validate_demultiplexed_fasta.py. Although the Description lists what conditions this script checks for, it doesn't say how the findings are reported, and the Output field on the documentation page is empty. From running it, I see that it creates a file named [myfastafile]_report.log in the directory of [myfastafile] ; it would be nice to have this stated explicitly in the Output field of the documentation (as is done for the validate_mapping_file.py script) so first-time users know what to look for.