add description of game rules to readme

README.md

@@ -17,3 +17,17 @@ Download a .exe file from [Releases](https://github.com/kevinsung/hexp2p/release
 ### Mac OS
 
 Download a .dmg file from [Releases](https://github.com/kevinsung/hexp2p/releases).
+
+## Rules of Hex
+
+The players (Black and White) take turns selecting a hexagon to fill with their color.
+A player wins when they have built a solid chain between the two edges of their color.
+The screenshot at the top of this page demonstrates a winning configuration for Black.
+
+### The swap rule
+
+Normally, the game is played using the swap rule in order to mitigate the advantage of
+playing first. Under the swap rule, Black makes the first move, and then White chooses
+whether or not to swap pieces with Black. If White chooses to swap pieces, then Black's
+move is replaced with the equivalent White move, and then it is Black's turn. Play then
+continues as normal.