Documentation: fix description for enabling hooks

Since f98f8cba (Ship sample hooks with .sample suffix, 2008-06-24) hooks
are not enabled by making them executable anymore, but by removing the
'.sample' suffix from the filename.
Signed-off-by: NMarkus Heidelberg <markus.heidelberg@web.de>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Documentation/gitrepository-layout.txt

@@ -134,7 +134,8 @@ hooks::
 	Hooks are customization scripts used by various git
 	commands.  A handful of sample hooks are installed when
 	'git-init' is run, but all of them are disabled by
-	default.  To enable, they need to be made executable.
+	default.  To enable, the `.sample` suffix has to be
+	removed from the filename by renaming.
 	Read linkgit:githooks[5] for more details about
 	each hook.
 

Documentation/glossary-content.txt

@@ -183,7 +183,8 @@ to point at the new commit.
 	and potentially aborted, and allow for a post-notification after the
 	operation is done. The hook scripts are found in the
 	`$GIT_DIR/hooks/` directory, and are enabled by simply
-	making them executable.
+	removing the `.sample` suffix from the filename. In earlier versions
+	of git you had to make them executable.
 
 [[def_index]]index::
 	A collection of files with stat information, whose contents are stored