add example to simple

apps/simple/markdown.ts

+import { MarkdownReader, VectorStoreIndex } from "llamaindex";
+
+async function main() {
+  // Load PDF
+  const reader = new MarkdownReader();
+  const documents = await reader.loadData("node_modules/llamaindex/README.md");
+
+  // Split text and create embeddings. Store them in a VectorStoreIndex
+  const index = await VectorStoreIndex.fromDocuments(documents);
+
+  // Query the index
+  const queryEngine = index.asQueryEngine();
+
+  const response = await queryEngine.query("What does the example code do?");
+
+  // Output response
+  console.log(response.toString());
+}
+
+main().catch(console.error);