fix(error): More closely match rustc's error style

[epage]

This is a follow up to #4385.

For example, rustc provides this error:

error[E0425]: cannot find value `arg1` in this scope
    --> src/builder/command.rs:4249:23
     |
4249 |                 arg = arg1.help("Print help");
     |                       ^^^^ help: a local variable with a similar name exists: `arg`

For more information about this error, try `rustc --explain E0425`.
error: could not compile `clap` due to previous error

So with both PRs, we went from

error: Found argument '--unknown' which wasn't expected, or isn't valid in this context

  If you tried to supply '--unknown' as a value rather than a flag, use '-- --unknown'

Usage: interop_hand_subcommand[EXE] add [NAME]...

For more information try '--help'

to

error: found argument '--unknown' which wasn't expected, or isn't valid in this context

  note: to pass '--unknown' as a value, use '-- --unknown'

Usage: interop_hand_subcommand[EXE] add [NAME]...

For more information, try '--help'.