Identify protocol version should be /polkadot

[tomaka]

The section mentioning the /ipfs/id/1.0.0 protocol should also mention that the protocolVersion field should be set to /polkadot.

Note that this is not the case at the moment, and I've opened paritytech/polkadot-sdk#505 so that Substrate does it.
This field is used just for debugging purposes, so it's a very minor point, but this field is supposed to be the same amongst the entire network.