update website text and design

web/app/header.tsx

@@ -0,0 +1,24 @@
+
+const navigation = [
+  { name: 'Github', href: 'https://github.com/jmorganca/ollama' },
+  { name: 'Download', href: '/download' },
+]
+
+export default function Header() {
+  return (
+    <header className="absolute inset-x-0 top-0 z-50">
+      <nav className="mx-auto flex items-center justify-between px-10 py-4">
+        <a className="flex-1 font-bold" href="/">
+          Ollama
+        </a>
+        <div className="flex space-x-8">
+          {navigation.map((item) => (
+            <a key={item.name} href={item.href} className="text-sm leading-6 text-gray-900">
+              {item.name}
+            </a>
+          ))}
+        </div>
+      </nav>
+    </header >
+  )
+}