NOTE:
This command is obsolete. It is kept because some client
programs and old computer programs still depend on it.
To promote to something besides a queen, use "=" notation,
as in "e8=n".
Here is the rest of the old "promote" help file:
Sets the promotion type. When a pawn reaches the 8th rank,
it will be promoted to a queen by default. You can change
this to a knight (k), bishop (b), or rook (r), by typing
"promote piece" where piece is k, b, r. You must type
this BEFORE moving the pawn. Your new promotion choice
remains in effect for the rest of the current game. You can
change the promotion type back to a queen with "promote q".
Yes, we know "k" is a dumb letter for knight, and "n" would be
better :)