update README

- add information about option paths

Author: Ffloriel

README.md

@@ -60,6 +60,23 @@ module.exports = {
 
 The options available in purgecss [Configuration](https://www.purgecss.com/configuration.html) are also avaiable in the webpack plugin with the exception of css and content.
 
+* #### paths
+
+With the webpack plugin, you can specified the content that should be analyized by purgecss with an array of filename. It can be html, pug, blade, ... files. You can use a module like `glob` or `glob-all` to easily get a list of files.
+
+```js
+const PurgecssPlugin = require('purgecss-webpack-plugin')
+const glob = require('glob')
+const PATHS = {
+  src: path.join(__dirname, 'src')
+}
+
+// In the webpack configuration
+new PurgecssPlugin({
+  paths: glob.sync(`${PATHS.src}/*`)
+})
+```
+
 * #### only
 
 You can specify entrypoints to the purgecss-webpack-plugin with the option only: