Document the config file real quick.

README.md

@@ -127,3 +127,9 @@ cp .\builddir\escape_turings_tarpit.exe . ;  .\escape_turings_tarpit.exe .\ "mes
 ```
 
 Now it's playing, so all you have to do is open one of the .cpp files, make a mistake, save it, and watch the game play.
+
+## Configuration
+
+There's a file `.tarpit.json` that configures everything for the game.  You can set your own sounds,
+the build directory, and the build command to use.  Just open it and you'll see.  If you don't want
+to hear me laughing at you then set the sounds to `nothing.mp3` and it'll be silent.