fix: update langchain-huggingface import and llama31 blog URL in hell…

[riyamit241]

What does this PR do?

Fixes three bugs in getting-started/RAG/hello_llama_cloud.ipynb:

1. Missing langchain-huggingface package
The notebook uses HuggingFaceEmbeddings but did not install langchain-huggingface.
In LangChain v0.1+, this class moved from langchain-community to the dedicated
langchain-huggingface package. Added !pip install langchain-huggingface to the
install cell.

2. Outdated import
Updated the import from:
from langchain_community.embeddings import HuggingFaceEmbeddings
to:
from langchain_huggingface import HuggingFaceEmbeddings
This reflects the current LangChain package structure and avoids a deprecation warning.

3. Wrong blog URL in WebBaseLoader
The notebook description says it loads the Llama 3.1 HuggingFace blog post, but the
code was loading the Llama 3 post (/blog/llama3). Updated to /blog/llama31 to
match the stated intent.

Testing

Verified all three changes manually by reviewing the notebook cells.