docs: Added more examples

examples/portkey.ts

+import { Portkey } from "llamaindex";
+
+(async () => {
+  const llms = [{
+
+  }]
+  const portkey = new Portkey({
+    mode: "single",
+    llms: [{
+      provider:"anyscale",
+      virtual_key:"anyscale-3b3c04",
+      model: "meta-llama/Llama-2-13b-chat-hf",
+      max_tokens: 2000
+    }]
+  });
+  const result = portkey.stream_chat([
+    { role: "system", content: "You are a helpful assistant." },
+    { role: "user", content: "Tell me a joke." }
+  ]);
+  for await (const res of result) {
+    process.stdout.write(res)
+  }
+})();