Add Python client example and corresponding README usage section

[SohamB-42]

This PR adds a minimal Python client example for interacting with the DIGIPIN API and documents it in the README.

Changes:

• New example file: examples/python/client.py
  • Simple CLI to:
    • Encode latitude/longitude to DIGIPIN using GET /api/digipin/encode
    • Decode DIGIPIN to coordinates using GET /api/digipin/decode
• New README section: "Using the API from Python"
  • Shows how to start the Node.js server and run the Python example.

Purpose:
To help Python developers quickly test and integrate the DIGIPIN API.