[docs] Add Request Deduplication example to main README

[AryanSharma48]

Problem

Request Deduplication is listed as a SmoothAPI feature, but the main
README Quickstart does not currently provide a simple example showing
how to enable it.

This makes it harder for users to discover how to use the feature.

What needs to be done

Add a Request Deduplication section to the main README.

The section should contain:

• A short explanation of what request deduplication does
• A simple code example
• The configuration required to enable it

The existing package documentation can be used as a reference.

Acceptance Criteria

• The main README contains a Request Deduplication section
• The section explains the feature clearly
• A working TypeScript/JavaScript example is included
• The example uses the current SmoothAPI API
• Markdown formatting is consistent with the rest of the README

Files to look at

• README.md
• packages/smooth-api-ts/README.md

Prerequisites

Basic Markdown and basic JavaScript/TypeScript.

Notes

The example should be copy-pasteable and should not introduce new APIs.