Add other methods of installing via cpan CLI for 'dzil authordeps' command

[SineSwiper]

Quick change

[rjbs]

I think this might be a bit too clever, and that maybe we want to just say "...or something like this."

If we're going to try to be this clever, it should work on Win32, etc., too.

[SineSwiper]

Oh, but it does work on Win32. I was just trying to capture the (little amount of) research I did to figure out how to get it to work.

[SineSwiper]

Something a little less clever would be adding the --skip-installed switch to the output. The existing command, without modifications, will download every module, even if the latest version already exists. This is quite a bit of a slowdown if you're just missing one module.