Add `println!("{:?}", Report::new(diagnostic))` pattern to README

[esoterra]

The fact that a Diagnostic can be printed to terminal by debug printing a Report from it is super useful and a nice trick for messing around with Miette. It should be added to the README.

[gavrilikhin-d]

Is there a reason why diagnostics are only pretty-printed with "{:?}" and not with "{}"?

[gavrilikhin-d]

Thanks for the issue, though. Spend a while looking for ways to print diagnostics manually, without miette::Result<>. XD