Fix Attachment.save wording nit.

discord/message.py

@@ -95,9 +95,10 @@ class Attachment:
         use_cached: :class:`bool`
             Whether to use :attr:`proxy_url` rather than :attr:`url` when downloading
             the attachment. This will allow attachments to be saved after deletion
-            more often, which is generally deleted right after the message is deleted.
-            Note that this can still fail to download deleted attachments if too much time
-            has passed.
+            more often, compared to the regular URL is generally deleted right after
+            the message is deleted. Note that this can still fail to download
+            deleted attachments if too much time has passed and it does not work
+            on some type of attachments.
 
         Raises
         --------