added some base code

flightscore/src/pages/not-found-page.ts

@@ -0,0 +1,12 @@
+import { LitElement, html } from 'lit';
+import { customElement } from 'lit/decorators.js';
+
+@customElement('not-found-page')
+export class NotFoundPage extends LitElement {
+  render() {
+    return html`
+      <h1>404 Not Found</h1>
+      <p>How did you get here?</p>
+    `;
+  }
+}