Final missions above ground (M30, co-op M20), surface option for versus matches, docs

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

README.md

@@ -72,7 +72,7 @@ to *step through shadows*, the chainbreaker to spin like a *whirlwind*.
 frost glows - and doors of wood, iron and magic. Lock them, and nobody gets through. Not even the giant. Well. Not for a while.
 
 **✨ Cast nasty spells.** Lightning, healing, seer's eye, cave-in, haste, stoneskin, gold rain, invisibility,
-plague and quake. Your scholars **research** them in the library - one discovery after another.
+plague, quake and frost. Your scholars **research** them in the library - one discovery after another.
 
 **🌫 Explore the dark.** Everything beyond your walls is black until your creatures go there.
 Somewhere out there: a cave of neutral **dwarves** guarding gold and gems - and sometimes a chest with the plans
@@ -84,6 +84,18 @@ of a dwarven **rune forge tower**. Islands in lava rivers. Mana springs. Creatur
   <br><i>Left: the forge and its little coglings. Right: prison, graveyard, arena, guard posts and the altar. Cosy.</i>
 </p>
 
+**🌳 Up into the daylight.** Some maps reach the surface: grass, birds, sunshine - disgusting - and forests your
+imps fell for **wood**, the second resource (down below only the odd giant mushroom gives some). Wood builds bridges
+and wooden doors. Raise walls again where you dug too much, burn the knights' wooden bridges, pull up your
+**drawbridges** when they come, freeze lava into obsidian to cross it - and roll **battering rams and catapults** out
+of your forge to break a fortress in the forest.
+
+<p align="center">
+  <img src="docs/screenshots/surface.png" width="400" alt="The cliff between the dungeon and a sunny forest above ground">
+  <img src="docs/screenshots/bridges.png" width="400" alt="A raised drawbridge, a lowered one, and obsidian on a lava river">
+  <br><i>Left: the world up there. Too bright. Right: a drawbridge up, a drawbridge down, and lava that thinks it is a floor.</i>
+</p>
+
 **👑 Other masters want your realm, too.** Mossgrim the Mouldy (green, smells like a wet cellar) and Lady Nightwell
 (blue, writes threatening letters on scented paper) dig their own dungeons in free play and in the campaign.
 And the humans attack *everybody*. Let them bite each other first.