Add a static site generator

There is no build for the element or site utilities like PrismJS yet, so this site only works locally at the moment.

docs-src/_includes/header.11ty.cjs

@@ -0,0 +1,7 @@
+module.exports = function(data) {
+  return `
+<header>
+  <h1>&lt;my-element></h1>
+  <h2>A web component just for me.</h2>
+</header>`;
+};