Add completions

[TaKO8Ki]

• [x] subcommands
• [x] flags
• [x] arguments

shell

• [x] zsh
• [x] bash
• [ ] fish

The rest of what to do is implement completions command for fish. https://github.com/TaKO8Ki/frum/blob/main/src/commands/completions.rs

ref: https://docs.rs/clap/2.31.0/clap/struct.App.html#method.gen_completions