Please provide documentation for --ignore for cli

How to translate:

  // ignore CSS rules
  ignore: {
    atrule: ['@font-face'],
    rule: [/some-regexp/],
    decl: (node, value) => /big-image\.png/.test(value),
  },

when using cli.

By the way, --dimensions W1xH1,W2xH2 didn't work for me while stated in #457:

Error: ConfigError: "dimensions" must be an array

Hopefully: --dimensions W1xH1 --dimensions W2xH2 did. Good to know we can use this option multiple times.

Best regards,