installing execcmd.el

[Kyle Jones]

Michael S. Balenger pointed out a rather egregious error in the
installation instructions for execcmd.el; a call to fmakunbound was
omitted.  The comment should read,

;; This package is autoloadable.  Use
;;    (fmakunbound 'execute-extended-command)
;;    (autoload 'execute-extended-command "execcmd" nil t)
;; in your .emacs file.