Breif description of the problem:
the tutorial of CLI has been out of date, and not work well under current clap ecosystem.
What is changed and how it works?
I append some help documentations for bb1's exercise and bump up project 1's rustc version.
actually I also consider the exercise doesn't match current rust ecosystem, but I have no idea which tutorial could work it out instead. maybe this is not a bad choice: https://medium.com/@ukpaiugochi0/building-a-cli-from-scratch-with-clapv3-fb9dc5938c82
What problem does this PR solve?
What is changed and how it works?
I append some help documentations for bb1's exercise and bump up project 1's rustc version. actually I also consider the exercise doesn't match current rust ecosystem, but I have no idea which tutorial could work it out instead. maybe this is not a bad choice: https://medium.com/@ukpaiugochi0/building-a-cli-from-scratch-with-clapv3-fb9dc5938c82