Notebook update fix and external drive compatibility

[ackagel]

Purpose

Fixes issue #477 and adds configurable external drive compatibility via the --external '/path/to/drive' or -e '/path/to/drive' argument flags.

Implementation

Moves some logic from update_notebooks.sh into start_docker.sh so that update_notebooks.sh is called conditionally. As for external drive compatibility, that just needs to be added to docker's filepaths in the preferences menu.

Remaining issues

The --external tag takes a path as a second argument in order to be compatible with multiple OS's. On macOS, this would always be /Volumes, while on Windows, it could be G:\\, F:\\, etc. I could see this being kind of annoying for macOS users, so a separate --mount_volumes | -m option could be added.

[ngreenwald]

Looks good. Did you test that update now works as intended, and that the external path works? What happens if the external path that is supplied has an error in it, or hasn't been added to docker preferences?

[alex-l-kong]

Not much else to add on top of Noah's comments.

[ackagel]

@ngreenwald update works as intended, and the external path works great for macOS. As for Windows, it's actually easier with the WSL2 backend, in that you don't need to share specific files in the Preferences menu. Updated the readme with that info.

Here's the consequence of a bad path on macOS: