git-log.txt: rewrite note on why "--" may be required

In its current form, the note talks about separating options from
"branch names" and "refnames" in the same sentence.  This is entirely
inaccurate, as <revision range> need not be a set of branch names or
ref names.  Rewrite it to use the word "revision range", to be
consistent with the SYNOPSIS.

Signed-off-by: Ramkumar Ramachandra <artagnon@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-log.txt

@@ -77,8 +77,8 @@ produced by --stat etc.
 	Simplification" below for details and other simplification
 	modes.
 +
-To prevent confusion with options and branch names, paths may need to
-be prefixed with "\-- " to separate them from options or refnames.
+Paths may need to be prefixed with "\-- " to separate them from
+options or the revision range, when confusion arises.
 
 include::rev-list-options.txt[]