add more background info for some protocol semantics

lib/hk-util.js

@@ -685,6 +685,14 @@ const handleGetHistory = function (Env, Server, seq, userId, parsed) {
             // If we're asking for a specific version (lastKnownHash) but we receive an
             // ENOENT, this is not a pad creation so we need to abort.
             if (err && err.code === 'ENOENT' && lastKnownHash) {
+/*
+    This informs clients that the pad they're trying to load was deleted by its owner.
+    The user in question might be reconnecting or might have loaded the document from their cache.
+    The owner that deleted it could be another user or the same user from a different device.
+    Either way, the respectful thing to do is display an error screen informing them that the content
+    is no longer on the server so they don't abuse the data and so that they don't unintentionally continue
+    to edit it in a broken state.
+*/
                 const parsedMsg2 = {error:'EDELETED', channel: channelName, txid: txid};
                 Server.send(userId, [0, HISTORY_KEEPER_ID, 'MSG', userId, JSON.stringify(parsedMsg2)]);
                 return;