Add clarifying paragraph on encryption page (#1672)

I wouldn't want to mislead people into thinking that encrypting and decrypting a save file locally on the player's computer can prevent editing and sharing of save files. It can't. The only way to prevent unauthorized editing and sharing of save data is to keep the save data on a remote server, and also running the game logic on that server instead of locally on the player's computer.

tutorials/io/encrypting_save_games.rst

@@ -74,3 +74,10 @@ some unique user identifier, for example:
 Note that ``OS.get_unique_id()`` only works on iOS and Android.
 
 This is all! Thanks for your cooperation, citizen.
+
+.. note:: This method cannot really prevent players from editing their savegames
+          locally, because since the encryption key is stored inside the game, the player
+          can still decrypt and edit the file themselves. The only way to prevent this
+          from being possible is to store the save data on a remote server where players
+          can only make authorized changes to their save data. If your game deals with
+          real money, you need to be doing this anyway.