apply: apply works outside a repository

The documentation for 'git apply' talks about applying a
patch/diff to the index and to the working tree, which seems
to imply that it will not work outside a git repository.

Actually 'git patch' works outside a repository (which can
be useful especially for applying binary or rename patches that
the standard "patch" utility cannot handle), so the documentation
should mention it.

Thanks to Junio for suggesting better wording.

Signed-off-by: Björn Gustavsson <bgustavsson@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-apply.txt

@@ -3,7 +3,7 @@ git-apply(1)
 
 NAME
 ----
-git-apply - Apply a patch on a git index file and/or a working tree
+git-apply - Apply a patch to files and/or to the index
 
 
 SYNOPSIS
@@ -20,8 +20,11 @@ SYNOPSIS
 
 DESCRIPTION
 -----------
-Reads supplied 'diff' output and applies it on a git index file
-and a work tree.
+Reads the supplied diff output (i.e. "a patch") and applies it to files.
+With the `--index` option the patch is also applied to the index, and
+with the `--cache` option the patch is only applied to the index.
+Without these options, the command applies the patch only to files,
+and does not require them to be in a git repository.
 
 OPTIONS
 -------