jackknifed_beta_diversity.py

Minor documentation change to address incorrect reference to a FASTA file which this script does not recieve.
split_libraries_fastq.py change resolves issue #993.

Modified the documentation to change -q20 to -q 20. Ignored the other comments since they seem to have been resolved elsewhere.
Merge pull request #1055 from wdwvt1/doc_changes

small documentation changes