Enhance documentation for search agent integration workflow

[n1colasf]

Description

This PR improves the documentation for search implementation by making the required workflow explicit and easy to follow from scratch.
It now clearly documents the required order: define a Retrieval, create a Retrieval Tool (Search), and register that search tool in the Agent.

Type of Change

• Documentation update

Related Issues

Fixes #25

Changes Made

• Added a dedicated section, Creating a Search from Scratch, with the full 3-step workflow in the docs.
• Clarified that the Retrieval must be defined first before creating the Search tool.
• Clarified that the Search must be included in the agent tools list, otherwise it will not be used.
• Kept examples minimal and clean to improve readability and reduce confusion.

Testing Done

• Tested manually

Checklist

• My code follows the project's style guidelines
• I have performed a self-review of my code
• I have made corresponding changes to the documentation
• My changes generate no new warnings

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