wrangling-genomics/04-variant_calling: download of fastq should have a download-free option

[JasonJWilliamsNY]

In general - I would like to avoid downloads, but that is a personal preference. If there is an alternative in the backup directory instructions should appear here.

[tobyhodges]

Bumping this, because @tadamus rightly points out that we should add an inline Instructor Note reminding Instructors that the FASTQ files are available in the .backup directory on AWS instances built from the AMI, after the transition to the Workbench.