fix Rmd download link

[bluegenes]

PR author:

• [ ] pull request is ready for review & merge

Things to check:

• [ ] tutorial resets working directory at beginning with a `cd ~/``
• [ ] tutorial contains relevant conda install -y commands at the beginning
• [ ] tutorial links to previous tutorial (at top) and next tutorial (at bottom)
• [ ] tutorial has learning objectives at top

[rociotmartinez]

ok!