Added a new ipynb notebook to show the Gemini integration with LlamaIndex and Chroma (google#287)

* Add an example for Gemini integration with LlamaIndex and Chroma

* notebook formatted using nbfmt

* colab and github buttons added

* Remove newline from GitHub button href

* Remove outputs from pip-install steps

* Pin the llama-index package to prevent breakages

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Co-authored-by: Mark McDonald <[email protected]>

Author: dev-nid