Documentation: correctly spell git worktree --detach

The option is “--detach”, but we accidentally spelled it “--detached” at
one point in the man page.

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Reported-by: Casey Rodarmor <casey@rodarmor.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-worktree.txt

@@ -51,7 +51,7 @@ Create `<path>` and checkout `<branch>` into it. The new working directory
 is linked to the current repository, sharing everything except working
 directory specific files such as HEAD, index, etc.
 +
-If `<branch>` is omitted and neither `-b` nor `-B` nor `--detached` used,
+If `<branch>` is omitted and neither `-b` nor `-B` nor `--detach` used,
 then, as a convenience, a new branch based at HEAD is created automatically,
 as if `-b $(basename <path>)` was specified.