Add and configure Tailwind CSS

Add and configure Tailwind CSS within the project, including adding npm
scripts for compiling the CSS, configuring purge settings, and adding
the `cssnano` library for minifying the CSS (which is run for production
builds).

tailwind.config.js

@@ -0,0 +1,13 @@
+module.exports = {
+  purge: {
+    content: ['templates/**/*.twig']
+  },
+  darkMode: false, // or 'media' or 'class'
+  theme: {
+    extend: {},
+  },
+  variants: {
+    extend: {},
+  },
+  plugins: [],
+}