Update README.md

README.md

@@ -3,7 +3,7 @@ MisaMino with more features. Tetrio attack table is on by default, others need t
 1. Tetrio attack table
 2. Garbage cap (in tetrio, you will at most accept 8 lines of garbage at a time, which is garbage cap = 8)
 3. Delayed attack (time in ms) (in tetrio or jstris, the garbage you sent will not show on opponent's garbage buffer right away) (you can still cancel these delayed garbage with your attack)
-4. Undo
+4. Undo (backspace)
 
 Download link: 
 You can find the link in the release page