Documentation: clarify information about 'ident' attribute

The documentation spoke of the attribute being set "to" a path; this can
mistakenly be interpreted as "the attribute needs to have its value set to
some kind of path". This clarifies things.

Signed-off-by: Jan Krüger <jk@jk.gs>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/gitattributes.txt

@@ -163,8 +163,8 @@ few exceptions.  Even though...
 `ident`
 ^^^^^^^
 
-When the attribute `ident` is set to a path, git replaces
-`$Id$` in the blob object with `$Id:`, followed by
+When the attribute `ident` is set for a path, git replaces
+`$Id$` in the blob object with `$Id:`, followed by the
 40-character hexadecimal blob object name, followed by a dollar
 sign `$` upon checkout.  Any byte sequence that begins with
 `$Id:` and ends with `$` in the worktree file is replaced