Define hyrule strategy swap rules

hyrule/README.md

@@ -35,10 +35,29 @@ captured by each player, the tallest player goes first. On each
 subsequent turn, the player with the most captured cards plays
 first. The play order then proceeds counter-clockwise.
 
-Each player selects a card and places it face-up in the center play
+When taking one's turn, the player may choose to either *play* or
+*swap*.
+
+#### strategy *play*
+
+When choosing to *play*, the player selects a card and places it
+face-up in the center play area. The remaining players take turns
+counter-clockwise, each placing a card face-up in the center play
 area. Precedence rules apply and the winning player takes all
 cards.
 
+#### strategy *swap*
+
+When choosing to *swap*, the player discards one card face-up in
+the discard pile (next to the stock pile) and then draws a card
+from the stock, which should be laying face-down. The goal here may
+be to take a chance at getting a better card than one is
+discarding, or to force the next player in the rotation to play, or
+both.
+
+> **NOTE**: a player may only choose to *swap* if the player on the
+> previous turn _did not swap_.
+
 ## precedence
 
 The following rules apply across suits with the exception of