new option and updated readme

[joshwnj]

Although we've discussed further improvements to the plugin architecture in #26 I'd like to add this new option in the meantime, since it's completely opt-in and doesn't affect existing behaviour.

@joshgillies pls take a look and merge if you're happy with it.

[joshgillies]

Sorry for the delay in getting onto this!

So I worry about this. In that in terms of an API it feels sloppy. Would it be better to change how the -u works, to basically not nuke the default PostCSS plugins for CSS Modules?

That being said, if the goal is to eventually re-architect the way plugins are handled anyway and assuming this PR solves problems people are having currently I'd be OK to +1 this.

Would it be much effort to tack on a CLI option to set this also? --after [pluginA, pluginB] maybe?

[joshwnj]

Yeah, I think longer-term it would be better to change the behaviour of -u so that by default the css modules plugins are preserved. Would you be happy with this as a non-breaking-change solution for now, and then aim to change -u when we go to 1.0?

I'll look at adding the --after CLI option.

[joshgillies]

Assuming we can get the CLI to feature parody with the Core API I'd be keen to release this.

Thanks for making this happen! 👍

[joshwnj]

@joshgillies I've added --after for CLI, please take a look and merge if you're happy with it.

[joshgillies]

Happy days! 😄

Merging!