Update paired_end.tex

changed trim option for both files

fastx_trimmer -Q 33 -f 1 -l 32 -i SRR023408_1.fastq -o SRR023408_trim1.fastq 
fastx_trimmer -Q 33 -f 1 -l 27 -i SRR023408_2.fastq -o SRR023408_trim2.fastq

with Annette