feat: add metadata for MultiPost documentation

- Introduce metadata object with title and description for the documentation

Author: cunoe

app/layout.tsx

@@ -3,6 +3,11 @@ import { RootProvider } from 'fumadocs-ui/provider';
 import { Inter } from 'next/font/google';
 import type { ReactNode } from 'react';
 
+export const metadata = {
+  title: 'MultiPost Documentation',
+  description: 'The documentation for MultiPost',
+};
+
 const inter = Inter({
   subsets: ['latin'],
 });