Add example notebook for financial document analysis with LlamaIndex

[Disiok]

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Summary

• Add example notebook for financial document analysis with LlamaIndex
• Add 2 10-K documents (PDFs) into data/examples/data/10k

This may have undesired effect in making repo bigger and thus git clone slower. Let me know if this is a big concern. Alternatives could be to use git-lfs to store this, or just point to the same files hosted at llama-index GitHub repo.