Update 2001/ctk/README.md with note about macOS

It unfortunately does not work well with the macOS default terminal
emulator (didn't test others). I also noted how one should use 'q' to
quit or else the terminal will be insane after you exit (which often
goes - I did say how to restore the terminal sanity too).

2001/ctk/README.md

@@ -23,6 +23,11 @@ make
 echo "Do or do not. There is no try."
 ```
 
+NOTE: this does not show well on the default terminal macOS. It's untested
+whether another terminal emulator will work. Make sure to hit 'q' to exit or
+else your terminal will be messed up (to restore it you can try `stty sane` or
+`reset`).
+
 ## Judges' comments:
 
 No matter how careful you are, this guy eventually crashes.  Most people