org-clock.el (org-program-exists): Fix docstring.

* org-clock.el (org-program-exists): Fix docstring.

Thanks to Sébastien Vauban for reporting this.

lisp/org-clock.el

@@ -694,7 +694,7 @@ Use alsa's aplay tool if available."
 	      (error (beep t) (beep t)))))))))
 
 (defun org-program-exists (program-name)
-  "Checks whenever we can locate program and launch it."
+  "Checks whenever we can locate PROGRAM-NAME using the `which' executable."
   (if (member system-type '(gnu/linux darwin))
       (= 0 (call-process "which" nil nil nil program-name))))