verilog/switches: Update Player 2 key documentation

271c2ea020
changed the Player 2 keys to standard ones in all platforms, and as part
of supporting a gamepad emulation, Z and X were repurposed as the player 1
gamepad.  T and R were allocated instead as the player 2 A/B buttons; see
03af8c2714/src/common/emu.ts (L341-L362)

presets/verilog/switches.v

@@ -5,7 +5,7 @@
 Switch test program.
 
 Player 1 Keys: arrow keys + space + shift
-Player 2 Keys: A/D/W/S + Z + X
+Player 2 Keys: A/D/W/S + T + R
 */
 module switches_top(clk, reset, hsync, vsync, 
                     switches_p1, switches_p2,