add comment to identity.js

lib/extra/identity.js

@@ -2,6 +2,10 @@ var base58check = require('./base58check');
 var constants   = require('./constants');
 var Hash        = require('./hash');
 
+
+/**
+ * See https://en.bitcoin.it/wiki/Identity_protocol_v1#Type_2_.28ephemeral.29
+ */
 function Identity(buf) {
   // TODO: instantiate identities without providing any configuration
   if (!(this instanceof Identity)) return new Identity(buf);