Add PurgeCSS config

Author: adamwathan

demo/tailwind.config.js

@@ -1,12 +1,6 @@
 module.exports = {
-  theme: {
-    typography: {
-      default: {
-        // bulletColor: 'red',
-        css: {},
-      },
-    },
-  },
+  purge: ['./demo/pages/**/*.{js,mdx}', './demo/components/**/*.{js,mdx}'],
+  theme: {},
   variants: {},
   plugins: [require('../src/index.js')],
 }