DM S18: Add a po hint about grammatical tense of some text

(cherry picked from commit 7ac222916a)

data/campaigns/Delfadors_Memoirs/scenarios/18_The_Portal_of_Doom.cfg

@@ -332,6 +332,9 @@
         [/message]
         [message]
             speaker=Delfador
+            #po: The same text is used both before and after closing the portal.
+            #po: Shown if the player kills Iliah-Malal instead of following the hints to run away,
+            #po: this is his last breath event, but he gets fully healed and the battle continues.
             message= _ "We cannot defeat him now. We must allow some time to pass after the portal has been closed. By then, his power will have weakened, rendering him vulnerable."
         [/message]
         # He gets a full heal, not an advance, otherwise we'd have to make sure we ported him to the next scenario properly