ENH: update atacama tutorial  (#87)
ENH: update atacama tutorial  (#87)

Update tutorial to cover only paired-end relevant commands and use smaller data set.
qiime2/docs,qiime2/docs,gregcaporaso/docs,qiime2/docs,jairideout/docs,gregcaporaso/docs,jairideout/docs,jairideout/docs,gregcaporaso/docs