adding documentation and example for 'only' param

Author: somebody32

README.md

@@ -27,35 +27,45 @@ const ExtractTextPlugin = require('extract-text-webpack-plugin')
 const PurgecssPlugin = require('purgecss-webpack-plugin')
 
 const PATHS = {
-  src: path.join(__dirname, 'src')
+    src: path.join(__dirname, 'src')
 }
 
 module.exports = {
-  entry: './src/index.js',
-  output: {
-    filename: 'bundle.js',
-    path: path.join(__dirname, 'dist')
-  },
-  module: {
-    rules: [
-      {
-        test: /\.css$/,
-        use: ExtractTextPlugin.extract({
-          fallback: 'style-loader',
-          use: 'css-loader?sourceMap'
+    entry: './src/index.js',
+    output: {
+        filename: 'bundle.js',
+        path: path.join(__dirname, 'dist')
+    },
+    module: {
+        rules: [
+            {
+                test: /\.css$/,
+                use: ExtractTextPlugin.extract({
+                    fallback: 'style-loader',
+                    use: 'css-loader?sourceMap'
+                })
+            }
+        ]
+    },
+    plugins: [
+        new ExtractTextPlugin('[name].css?[hash]'),
+        new PurgecssPlugin({
+            paths: glob.sync(`${PATHS.src}/*`)
         })
-      }
     ]
-  },
-  plugins: [
-    new ExtractTextPlugin('[name].css?[hash]'),
-    new PurgecssPlugin({
-      paths: glob.sync(`${PATHS.src}/*`)
-    })
-  ]
 }
 ```
 
+you can also limit plugin to certain entrypoints via `only` param:
+
+```
+new PurgecssPlugin({
+    paths: glob.sync(`${PATHS.src}/*`),
+    styleExtensions: ['.css'],
+    only: ['bundle', 'vendor']
+})
+```
+
 ## Contributing
 
 Please read [CONTRIBUTING.md](./.github/CONTRIBUTING.md) for details on our code of conduct, and the process for submitting pull requests to us.
@@ -66,8 +76,8 @@ We use [SemVer](http://semver.org/) for versioning.
 
 ## Acknowledgment
 
-Purgecss was originally thought as the v2 of purifycss. And because of it, it is greatly inspired by it.  
-The plugins such as purgecss-webpack-plugin are based on the purifycss plugin.  
+Purgecss was originally thought as the v2 of purifycss. And because of it, it is greatly inspired by it.
+The plugins such as purgecss-webpack-plugin are based on the purifycss plugin.
 Below is the list of the purifycss repositories:
 
 * [purifycss](https://github.com/purifycss/purifycss)

examples/simple-with-exclusion/.vscode/settings.json

@@ -0,0 +1,3 @@
+// Place your settings in this file to overwrite default and user settings.
+{
+}

examples/simple-with-exclusion/dist/bundle.css

@@ -0,0 +1,11 @@
+.hello {
+  color: red;
+}
+
+.whitelisted {
+  color: green;
+}
+
+md\:w-2\/3 {
+  color: red;
+}