cellranger session - command line issues

[tavareshugo]

It's very common for participants to struggle with the command line.
Can we streamline this section of the materials, perhaps so that it requires writing less code.

Some ideas:

• drop VS Code as an editor (that's an extra cognitive load) and just using nano/gedit from the terminal.
• eliminate exercise 1 and instead provide an already-written script. So they can be shown the code in the script and just run it with bash.
• for exercise 2 have a pre-written script skeleton as well, so all they have to do is edit the paths in gedit/nano. Hopefully that avoids things like spacing typos and so on.