Merge before assign

[jonthegeek]

When the assign script runs, it uses whatever the user had outside their curated directory for the rest of the structure. It should use the scripts (etc) from master (or main, once we fix that), and only the data from the user's branch.

Ideally their submission should only be their own directory, actually. So set it up that way (check out master then put their submission in /data/curated then do the things). Update the instructions to match that (they'll check out a branch other than master to start and shouldn't have to download the full repo).