refactor: Rename Deno main file to index.ts and update import

deno/index.ts

@@ -0,0 +1,10 @@
+export function add(a: number, b: number): number {
+  return a + b;
+}
+
+// Learn more at https://docs.deno.com/runtime/manual/examples/module_metadata#concepts
+if (import.meta.main) {
+  console.log("Add 2 + 3 =", add(2, 3));
+}
+
+Deno.serve({ hostname: "0.0.0.0", port: 8000 }, () => new Response("Hello, world!"));