fix: publicPath function examples filename should include [path]

To demonstrate why the dynamic relative path is necessary.

README.md

@@ -90,9 +90,9 @@ const MiniCssExtractPlugin = require("mini-css-extract-plugin");
 module.exports = {
   plugins: [
     new MiniCssExtractPlugin({
-      // Options similar to the same options in webpackOptions.output
-      // both options are optional
-      filename: "[name].css",
+      // Filename includes [path] so we use the publicPath function (below) to dynamically
+      // create publicPath relative to the source CSS file.
+      filename: "[path]/[name].css",
       chunkFilename: "[id].css"
     })
   ],

test/cases/function-publicpath/webpack.config.js

@@ -29,7 +29,7 @@ module.exports = {
   },
   plugins: [
     new Self({
-      filename: '[name].css',
+      filename: '[path]/[name].css',
     }),
   ],
 };