ocs: clarify what load_dotenv() does in README

[cybercoded]

This PR updates the README to explicitly describe what load_dotenv() does.

• Makes it clear that load_dotenv() reads key-value pairs from a .env file and sets them in os.environ.
• States that existing environment variables are not overridden unless override=True is passed.
• Removes redundant wording for clarity.

This addresses the documentation gap highlighted in issue #571.

Fixes #571