configs are hard to get working

From the #tilt channel:

I'm using tilt up -- --to-run frontend and then config.define_string_list("to-run", args=True) and print(cfg.get('to-run', [])) and I get Error: flag provided but not defined: -to-run

When I read the documentation myself, I was not able to get this to work, or adequately explain why it didn't work. (The problem is that args=True means "don't use the flag name on the command-line")

As I see it, there are a couple different problems here that might be worth separating:

• The error message is poor. Tilt knows that to-run is a positional argument. Why can't it tell me that?
• The documentation doesn't link to any working examples. When I tried to make a working example myself, I was not able to. Multiple people have complained that they were not able to get this working without hand-holding from the Tilt team

Start by reproducing tilt up -- --to-run frontend with config.define_string_list("to-run", args=True) and compare it with the documented configuration behavior. Review the CLI configuration documentation and any working examples you can locate; done means the positional-argument behavior is clearly explained, a working example is provided, and the error identifies the issue usefully.