Saving a command file needs both `requires_dir` and `save_files` keys

[gcapes]

The documentation says that you need a save_files key, which makes sense, but that only works if you also have a requires_dir key too. Without either key, or with just the save_files key, the files are saved to artifacts/submissions/0/tmp. Only when using both keys, are the named files saved under artifacts/tasks.

The docs kinda suggest that save_files saves files, but there's nothing to explain that it only works if you use requires_dir. requires_dir doesn't have any explanation.

In the first instance, the docs should reflect how things actually work, but longer term, it would make more sense if save_files did what the name suggests without needing an undocumented helper key (requires_dir).