SRA Toolkit commands in the README

[evanbiederstedt]

Hi Heng Li

It might be good to update the README with respect to downloading C. elegans

The following doesn't work:

$ fastq-dump --split-spot SRR065390.lite.sra
fastq-dump.2.8.1 err: item not found while constructing within virtual database module - the path 'SRR065390.lite.sra' cannot be opened as database or table

The following does work:

$  fastq-dump --split-spot SRR065390

Thanks!