Update HelloLlamaCloud.ipynb (#260)

demo_apps/HelloLlamaCloud.ipynb

@@ -35,7 +35,7 @@
    "metadata": {},
    "outputs": [],
    "source": [
-    "!pip install langchain replicate sentence-transformers chromadb"
+    "!pip install langchain replicate sentence-transformers chromadb pypdf"
    ]
   },
   {