README is out of date: `print_schedule` -> `print_schedule_graph`

[andriyDev]

The README is out of date. print_schedule needs to be replaced with print_schedule_graph.

This could be made more robust using #![doc = include_str!("../README.md")] in the crate to include the README as the docstring for the crate. Then we could test that the README compiles with cargo test --doc as a Github action! But that's probably something that should be addressed in another issue.