fix(complete): Make the two examples consistent
fix(complete): Make the two examples consistent

The derive-based example has a `///` comment on one argument, which
ends up as a description for the argument in the generated completion
scripts. Let's switch to `//` so the two scripts produce the same
output (except for the binary name), so they're easy to compare.

clap-rs/clap,clap-rs/clap,clap-rs/clap