Update HelloLlamaCloud.ipynb

added pypdf to !pip install - required for cell containing:

from langchain.document_loaders import PyPDFLoader
loader = PyPDFLoader("https://arxiv.org/pdf/2307.09288.pdf")
docs = loader.load()

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"
    ]
   },
   {