[FEATURE] Mention EasyTalk as alternative schema library in your docs.

[sergiobayona]

Scope check

• This is core LLM communication (not application logic)
• This benefits most users (not just my use case)
• This can't be solved in application code with current RubyLLM
• I read the Contributing Guide

Due diligence

• I searched existing issues
• I checked the documentation

What problem does this solve?

Mention the EasyTalk gem in your chat.md page as an alternative schema library for users who need additional features like ActiveModel validations.

Proposed solution

Insert:

Alternative: EasyTalk is another Ruby DSL for JSON Schema that also generates ActiveModel validations. Its schemas work directly with ruby_llm's with_schema method.
{: .note }

Just above https://rubyllm.com/chat/#using-manual-json-schemas section

Why this belongs in RubyLLM

It enriches the RubyLLM ecosystem by providing additional tools to work with.