docs(core): Document byte format of `PeerId`
PeerId data is more than just a multihash of the public key.
See discussion:
@@ -34,8 +34,8 @@ const MAX_INLINE_KEY_LENGTH: usize = 42;
/// Identifier of a peer of the network.
///
-/// The data is a multihash of the public key of the peer.
-/// See the [spec](https://github.com/libp2p/specs/blob/master/peer-ids/peer-ids.md) for more information.
+/// The data is a CIDv0 compatible multihash of the protobuf encoded public key of the peer
+/// as specified in [specs/peer-ids](https://github.com/libp2p/specs/blob/master/peer-ids/peer-ids.md).
#[derive(Clone, Copy, Eq, Hash, Ord, PartialEq, PartialOrd)]
pub struct PeerId {
multihash: Multihash,
