[docs] Document synchronous timeout limitation in Python

[AryanSharma48]

Problem

SmoothAPI's Python implementation supports request timeouts for async
usage, while synchronous usage does not support the same timeout_ms
configuration.

The current documentation mentions that request timeouts are async-only,
but this limitation could be made more explicit to prevent users from
assuming that timeout_ms works with synchronous requests.

What needs to be done

Improve the Python README by explicitly documenting the synchronous
timeout limitation.

The documentation should explain:

• That SmoothAPI's timeout_ms configuration is async-only
• What happens when it is used with synchronous functionality
• That users of synchronous requests can use the request library's own
  timeout functionality where appropriate

Acceptance Criteria

• The async-only limitation is clearly documented
• The synchronous behavior is explained
• The documentation provides a useful alternative for synchronous users
• The wording is clear and user-friendly
• No implementation behavior is changed

Files to look at

• packages/smooth-api-py/README.md
• packages/smooth-api-py/smooth_api/__init__.py

Prerequisites

Basic Markdown.

Notes

This issue is documentation-only. Do not modify the timeout implementation.