docs(plugins): add purgecss webpack plugin (#93)

* add purgecss webpack plugin

* change description

Author: Ffloriel

README.md

@@ -197,7 +197,7 @@ Inspired by the [awesome](https://github.com/sindresorhus/awesome) list. Feel fr
 - [Friendly errors](https://github.com/geowarin/friendly-errors-webpack-plugin) - Recognizes certain classes of webpack errors and cleans, aggregates and prioritizes them. -- *Maintainer*: `Geoffroy Warin` [![Github][githubicon]](https://github.com/geowarin)
 - [FileManager Webpack Plugin](https://github.com/gregnb/filemanager-webpack-plugin) - Copy, move, delete files and directories before and after Webpack builds -- *Maintainer*: `Gregory Nowakowski` [![Github][githubicon]](https://github.com/gregnb)
 - [Duplicate Package Checker Webpack Plugin](https://github.com/darrenscerri/duplicate-package-checker-webpack-plugin) - Warns you when multiple versions of the same package exist in your bundle -- *Maintainer*: `Darren Scerri` [![Github][githubicon]](https://github.com/darrenscerri)
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+- [PurgeCSS Webpack Plugin](https://github.com/FullHuman/purgecss-webpack-plugin) - A plugin to remove unused css with purgecss -- *Maintainer*: `Floriel Fedry` [![Github][githubicon]](https://github.com/Ffloriel)
 
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