[templates/d,flowershow#1][s]: home page runs off markdown content/in…

…dex.md rather than pages/index.js.

* Convert from catch-all route to optional catch-all route.

templates/default/content/index.md

@@ -0,0 +1,3 @@
+# Flowershow Default Template
+
+## A starter template for Next.JS with Tailwind and MDX

templates/default/pages/[...slug].js → templates/default/pages/[[...slug]].js

@@ -14,7 +14,8 @@ export default function Page({ body, ...rest }) {
 }
 
 export async function getStaticProps({ params }) {
-  const urlPath = params.slug.join("/");
+  // params.slug is undefined for root index page
+  const urlPath = params.slug ? params.slug.join("/") : '';
   const page = allPages.find((p) => p.url === urlPath);
   return { props: page };
 }