Add example with fastify-type-provider-zod for docs

[ViniciusLeviVL]

This PR enhances the project documentation by adding a new use case for body validation using Zod in conjunction with fastify-type-provider-zod. The example demonstrates how to validate multipart form-data requests, including custom refinements for file size and type validation.

Changes Made:

• Added a new section in the README.md titled "Zod Schema body validation".
• Provided a step-by-step guide for integrating Zod with Fastify.
• Included example code for setting up multipart validation with zod.
• Added refinements examples for file size (maximum 10MB) and type (only images).
• Clarified limitations with Zod (FormData support) and fastify-type-provider-zod (Swagger support).

Checklist

• Documentation is changed or added.
• Verified example code is functional.

[ViniciusLeviVL]

Issue #559

[Fdawgs]

This would be better as an actual example in the examples directory, rather than dedicating a section of the docs to it.

[ViniciusLeviVL]

This would be better as an actual example in the examples directory, rather than dedicating a section of the docs to it.

I agree that dedicating a section to this might clutter the documentation, but having it only as an example in the examples directory might not reach as many people due to SEO, as many users search directly in the browser. I believe the best option would be to include the example along with a reference, link, or something similar to the examples directory. What do you think about this?