docs: add index at root

docs/src/content/docs/index.mdx

@@ -0,0 +1,18 @@
+---
+title: Domain Watchdog
+description: An app that uses RDAP to collect publicly available info about domains, track their history, and purchase then when they expire
+template: splash
+hero:
+  tagline: Your companion in the quest for domain names 🔍
+  image:
+    file: ../../assets/logo.png
+  actions:
+    - text: Get started
+      link: /en/features
+      icon: right-arrow
+    - text: Demo
+      link: https://demo.domainwatchdog.eu
+      icon: external
+      variant: minimal
+---
+