additional documentation for libsql sync example

[OrthelT]

Summary

This PR improves the documentation and example for using libSQL with a synced Turso database. The updates make setup clearer and replaces command line environment variables with a .env file for easier configuration.

Changes

README.md

• Updated install instructions:
  • Added python-dotenv dependency to support loading .env file.
• Added Requirements section explaining an existing Turso cloud database and .env file are needed.
• Expanded setup steps to include creating a new db in Turso CLI:
  • Included turso db create, turso db show, and turso db tokens create.
  • Added example .env file snippet.
• Simplified run instructions:
  • Now uses python3 main.py and a '.env' file in place of inline environment variables.

main.py

• Added a detailed docstring with more explicit instructions, requirements and setup steps.
• Added from dotenv import load_dotenv and load_dotenv() for compatibility with '.env' file.

Motivation

The original example was functional but assumed prior knowledge that could frustrate new users:

• It implicitly required an existing Turso database, without guidance on how to create one.
• There were no instructions for obtaining or using Turso database credentials.
• Users were expected to inline environment variables at runtime, which is less typical in Python and inconsistent with common practice.

Because embedded sync is a common entry point for developers new to libSQL and Turso, this update improves usability by:

• Providing a complete, self-contained setup workflow for first-time users.
• Adding .env support via python-dotenv to align with Python best practices for managing credentials.

Testing

• Verified that the example runs successfully using a .env file with valid TURSO_DATABASE_URL and TURSO_AUTH_TOKEN values.
• Confirmed that the local database syncs correctly, the users table is created, and expected query results are printed.