postcss-modules-values is now included in default plugins

[IanVS]

The readme does not mention that postcss-modules-values is now included in the default set of plugins (from css-modules-loader-core).

Running with --after postcss-modules-values was giving an error, and it took me a while to figure out why. Updating the readme may avoid such headaches for others.

[joshwnj]

thanks for bringing this up @IanVS . Would you be interested in making a PR to update the readme?

[IanVS]

Sure thing, will do it tonight.