bug#23541: 25.0.93; cl-loop: fix documentation string

[Tino Calancha]

On for clauses 'by' is optional.

In GNU Emacs 25.0.93.1 (x86_64-pc-linux-gnu, GTK+ Version 2.24.30)
Repository revision: 6de0715f5467d4b925e2dfe082174529ace3b174

> From ee4d5ebf3d3aa885e99ee65d592d77a1008650ca Mon Sep 17 00:00:00 2001
From: Tino Calancha <f92capac@gmail.com>
Date: Mon, 16 May 2016 00:12:19 +0900
Subject: [PATCH] ; * lisp/emacs-lisp/cl-macs.el (cl-loop): Fix doc. string

---
 lisp/emacs-lisp/cl-macs.el | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/lisp/emacs-lisp/cl-macs.el b/lisp/emacs-lisp/cl-macs.el
index 68abe67..2cb821e 100644
--- a/lisp/emacs-lisp/cl-macs.el
+++ b/lisp/emacs-lisp/cl-macs.el
@@ -851,9 +851,9 @@ cl-loop
   "The Common Lisp `loop' macro.
 Valid clauses include:
   For clauses:
-    for VAR from/upfrom/downfrom EXPR1 to/upto/downto/above/below EXPR2 by 
EXPR3
+    for VAR from/upfrom/downfrom EXPR1 to/upto/downto/above/below EXPR2 [by 
EXPR3]
     for VAR = EXPR1 then EXPR2
-    for VAR in/on/in-ref LIST by FUNC
+    for VAR in/on/in-ref LIST [by FUNC]
     for VAR across/across-ref ARRAY
     for VAR being:
       the elements of/of-ref SEQUENCE [using (index VAR2)]
--
2.8.1