docs: Add beta notice

docs/src/pages/index.module.css

@@ -30,6 +30,15 @@
     border: 1px solid var(--ifm-color-warning-darkest);
 }
 
+.betaNotice {
+    max-width: 600px;
+    margin: 0 auto 4rem;
+    padding: 12px;
+    border-radius: 6px;
+    border: 1px solid var(--ifm-color-warning-darkest);
+    background-color: #d99e0022;
+}
+
 .description {
     margin: 1rem 0;
     font-size: 1.3rem;

docs/src/pages/index.tsx

@@ -44,6 +44,16 @@ export default function Home(): JSX.Element {
                 </div>
             </div>
             <main>
+                <div>
+                    <p className={styles.betaNotice}>
+                        This is a developer preview of our new documentation site. If you have any feedback,
+                        please comment on{' '}
+                        <a href="https://github.com/vendure-ecommerce/vendure/issues/2299" target="_blank">
+                            this GitHub issue
+                        </a>{' '}
+                        or let us know via our <a href="https://vendure.io/community">Discord community</a>.
+                    </p>
+                </div>
                 <div className={styles.ctaButtons}>
                     <Link className="button button--secondary" to="/guides/getting-started/installation/">
                         Get Started