Updates CONTRIBUTING.md to add installation of uv in development setup

[Harsh-2909]

Description

• Summary of changes: This PR adds a point in CONTRIBUTING.md file for installing uv when setting up a development environment.
• Related issues: This PR is not connected to any issue.
• Motivation and context: I just made a fork of this repo to understand and contribute to this project. When I was setting up development environment from the instructions, the setup was incomplete due to uv not being installed in my system.
• Environment or dependencies: No changes there
• Impact on metrics: NA.

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Type of change

Please check the options that are relevant:

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Model update (Addition or modification of models)
• Other (please describe): Documentation change

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Checklist

• Adherence to standards: Code complies with Agno’s style guidelines and best practices.
• Formatting and validation: You have run ./scripts/format.sh and ./scripts/validate.sh to ensure code is formatted and linted.
• Self-review completed: A thorough review has been performed by the contributor(s).
• Documentation: Docstrings and comments have been added or updated for any complex logic.
• Examples and guides: Relevant cookbook examples have been included or updated (if applicable).
• Tested in a clean environment: Changes have been tested in a clean environment to confirm expected behavior.
• Tests (optional): Tests have been added or updated to cover any new or changed functionality.

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[dirkbrnd]

Thanks for the addition!