Added some instructions to README.

README.md

@@ -33,6 +33,7 @@ There are minor graphics- and gameplay-related issues, and possibly occasional c
 * experimental high framerate support (up to 240 FPS):
   * set `Game.TickRateDivisor` to `0` in `pd.ini` to activate;
   * in practice the game will have issues running faster than ~165 FPS, so use VSync or `Video.FramerateLimit` to cap it.
+* emulate the Transfer Pak functionality the game has on the Nintendo 64 to unlock some cheats automatically.
 
 Currently only 32-bit platforms are supported, namely x86 Windows and Linux.  
 Note that 32-bit binaries will still work on 64-bit versions of those platforms,
@@ -58,6 +59,8 @@ If you want to use a PAL or JPN ROM instead, put them into the `data` directory
 * PAL: ROM name `pd.pal-final.z64`, EXE name `pd.pal.exe`.
 * JPN: ROM name `pd.jpn-final.z64`, EXE name `pd.jpn.exe`.
 
+Optionally, you can also put your Perfect Dark for GameBoy Color ROM named `pd.gbc` in the `data` directory if you want to emulate having the Nintendo 64's Transfer Pak and unlock some cheats automatically.
+
 Additional information can be found in the [wiki](https://github.com/fgsfdsfgs/perfect_dark/wiki).
 
 A GPU supporting OpenGL 3.0 or above is required to run the port.