doc: clarify tls.tlsSocket.getCipher().version
The getCipher() returns a tuple that includes protocol version string. This string refers to the minimum protocol version string, as per documentation. What is missing is a reference to the documentation where to get the negotiated cipher for the socket connection and a clearer example.
Fixes: https://github.com/nodejs/node/issues/43406
This PR is in response to recommendation to clarify this part of the documentation.