Adds a cookbook for File Search (#1034)

Author: markmcd

README.md

@@ -19,8 +19,8 @@ We also showcase **Demos** in separate repositories, illustrating end-to-end app
 
 Here are the recent additions and updates to the Gemini API and the Cookbook: 
 
+* **File Search:** Discover how to ground generations in your own data in a hosted RAG system with the [File Search quickstart](./quickstarts/File_Search.ipynb) [![Colab](https://storage.googleapis.com/generativeai-downloads/images/colab_icon16.png)](https://colab.research.google.com/github/google-gemini/cookbook/blob/main/quickstarts/File_Search.ipynb). 
 * **Grounding with Google Maps:** Get started using factual geographical data from 📍 Google Maps in your apps! See the Google Maps section of the [Grounding Guide](./quickstarts/Grounding.ipynb) [![Colab](https://storage.googleapis.com/generativeai-downloads/images/colab_icon16.png)](https://colab.research.google.com/github/google-gemini/cookbook/blob/main/quickstarts/Grounding.ipynb).
-* **Gemini 2.5 models:** Explore the capabilities of the latest Gemini 2.5 models (Flash and Pro)! See the [Get Started Guide](./quickstarts/Get_started.ipynb) [![Colab](https://storage.googleapis.com/generativeai-downloads/images/colab_icon16.png)](https://colab.research.google.com/github/google-gemini/cookbook/blob/main/quickstarts/Get_started.ipynb) and the [thinking guide](./quickstarts/Get_started_thinking.ipynb) [![Colab](https://storage.googleapis.com/generativeai-downloads/images/colab_icon16.png)](https://colab.research.google.com/github/google-gemini/cookbook/blob/main/quickstarts/Get_started_thinking.ipynb) since they are all thinking ones.
 * **Gemini Image** (aka. 🍌 nano banana): Use [Gemini's native image generation](./quickstarts/Image_out.ipynb) [![Colab](https://storage.googleapis.com/generativeai-downloads/images/colab_icon16.png)](https://colab.research.google.com/github/google-gemini/cookbook/blob/main/quickstarts/Image_out.ipynb) capabilities to edit images with high consistency or generate visual stories.
 * **Veo 3.1**: Get started with our video generation model with this [Veo guide](./quickstarts/Get_started_Veo.ipynb), including image-to-videos and video extension! [![Colab](https://storage.googleapis.com/generativeai-downloads/images/colab_icon16.png)](https://colab.research.google.com/github/google-gemini/cookbook/blob/main/quickstarts/Get_started_Veo.ipynb)
 * **Gemini Robotics-ER 1.5**: Learn about this new Gemini model specifically for spatial understanding and reasoning for [robotics applications](./quickstarts/gemini-robotics-er.ipynb). [![Colab](https://storage.googleapis.com/generativeai-downloads/images/colab_icon16.png)](https://colab.research.google.com/github/google-gemini/cookbook/blob/main/quickstarts/gemini-robotics-er.ipynb)