The easiest way to install it (but may make uninstalling more difficult later) is to copy that code and open config\autoexec.cfg for editing (like a text file). Paste the code in that file. Now in-game you can type
/showmenu "k/b"
and the menu will pop up.
If you want to make it easier, add something like
in autoexec.cfg. Then you can type
/kb
and the menu will pop up.
/showmenu "k/b"
and the menu will pop up.
If you want to make it easier, add something like
[SELECT ALL] Code:
alias kb [showmenu "k/b"]
/kb
and the menu will pop up.