lesson 2 explain output object and add exercise: renaming workflow output

[mr-c]

• [ ] explain the CWL output object that is already shown
  • [ ] each File is listed with properties (explain them)
  • [ ] we are explictly told the location of each output file and directory, unlike when using docker or most tools themselves
  • [ ] each output has a name that corresponds with our workflow outputs sections; these should meaningful because sometimes the filenames are cryptic
• [ ] qc_html is not a great name, add exercise on naming it to quality_report