readme - add some more plugins to the list

* [broccoli-autoprefixer](https://github.com/sindresorhus/broccoli-autoprefixer)
* [broccoli-svgo](https://github.com/sindresorhus/broccoli-svgo)
* [broccoli-csso](https://github.com/sindresorhus/broccoli-csso)
* [broccoli-htmlmin](https://github.com/sindresorhus/broccoli-htmlmin)
* [broccoli-jade](https://github.com/sindresorhus/broccoli-jade)
* [broccoli-uncss](https://github.com/sindresorhus/broccoli-uncss)
* [broccoli-strip-debug](https://github.com/sindresorhus/broccoli-strip-debug)
* [broccoli-less](https://github.com/sindresorhus/broccoli-less)
* [broccoli-stylus](https://github.com/sindresorhus/broccoli-stylus)
* [broccoli-traceur](https://github.com/sindresorhus/broccoli-traceur)
* [broccoli-sweetjs](https://github.com/sindresorhus/broccoli-sweetjs)
* [broccoli-closure-compiler](https://github.com/sindresorhus/broccoli-closure-compiler)
* [broccoli-regenerator](https://github.com/sindresorhus/broccoli-regenerator)
* [broccoli-defeatureify](https://github.com/sindresorhus/broccoli-defeatureify)
* [broccoli-nunjucks](https://github.com/sindresorhus/broccoli-nunjucks)
* [broccoli-dust](https://github.com/sindresorhus/broccoli-dust)
* [broccoli-strip-json-comments](https://github.com/sindresorhus/broccoli-strip-json-comments)
* [broccoli-es6-transpiler](https://github.com/sindresorhus/broccoli-es6-transpiler)


Though might just be easier to link to https://www.npmjs.org/browse/keyword/broccoli-plugin