EI S10: Switch shroud to fog

The scenario was otherwise generally unwinnable on the first attempt. Although
the extra turns in added in ab900b0 help with
that, it's still worth changing to fog instead of shroud.

Part of #4145

data/campaigns/Eastern_Invasion/scenarios/10_Lake_Vrug.cfg

@@ -29,7 +29,8 @@
         controller=human
         team_name=good
         user_team_name=_"Wesnothians"
-        shroud=yes
+        shroud=no
+        fog=yes
         {GOLD 300 260 220}
         {FLAG_VARIANT loyalist}
     [/side]
@@ -157,6 +158,11 @@
             speaker=Gweddry
             message= _ "Very well, we will take care of the trolls and gryphons. Search the library and may you find us an answer. Onward!"
         [/message]
+        {HIGHLIGHT_IMAGE 12 4 items/gohere.png ()}
+        [label]
+            x,y=12,4
+            text = _ "The stronghold"
+        [/label]
     [/event]
 
     #give the player a hint about mountainous terrain