Clearify the documentation for core.ignoreStat

The previous documentation didn't make it clear that the
"assume unchanged" was on per file basis, and not a global
flag.

Signed-off-by: Marius Storm-Olsen <marius@trolltech.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/config.txt

@@ -205,10 +205,13 @@ Can be overridden by the 'GIT_PROXY_COMMAND' environment variable
 handling).
 
 core.ignoreStat::
-	The working copy files are assumed to stay unchanged until you
-	mark them otherwise manually - Git will not detect the file changes
-	by lstat() calls. This is useful on systems where those are very
-	slow, such as Microsoft Windows.  See linkgit:git-update-index[1].
+	If true, commands which modify both the working tree and the index
+	will mark the updated paths with the "assume unchanged" bit in the
+	index. These marked files are then assumed to stay unchanged in the
+	working copy, until you	mark them otherwise manually - Git will not
+	detect the file changes	by lstat() calls. This is useful on systems
+	where those are very slow, such as Microsoft Windows.
+	See linkgit:git-update-index[1].
 	False by default.
 
 core.preferSymlinkRefs::