Explicitly document data collection and telemetry for the CLI

[alessio-locatelli]

I think adding at least a small note to the README.md would be professional and user-friendly. Below are example texts you can copy and adapt to your case:

• The CodeCrafters CLI does not collect any data or telemetry.
• The CodeCrafters CLI reads your local <...> and sends <...>.
• The CodeCrafters CLI uses OpenTelemetry. To opt out, set ...