Update docs

[Obi-Dann]

As per suggestions from @adriangodong in #7:

Thank you for bringing this package up to the latest version!
While working with this package, I found several issues that can be clarified in the documentation:

• This package no longer replaces css-loader, but it has to be added after css-loader
• There's mentioned of peer dependency to css-loader, but due to the requirement above, this is no longer relevant
• css-loader will need to be configured to output CSS Modules (e.g. options: { modules: true; })

Changes:

• Adding Upgrade guide from v1 to README
• Remove css-loader from peer dependencies
• Updating examples with the correct use of CSS Modules options: { modules: true; }

[CoericK]

The css-loader option

namedExport: true

Is not longer supported on css-loader v3.x

That will trigger an error

options has an unknown property 'namedExport'. These properties are valid:
   object { url?, import?, modules?, sourceMap?, importLoaders?, localsConvention?, onlyLocals? }

[Obi-Dann]

Good point, going to remove it, thanks!