sort: improve usage wording

* src/sort.c (usage): Mention that -k defaults to end of line if
POS2 omitted.
* THANKS: Update.
Reported by Tim Ryan.

Signed-off-by: Eric Blake <ebb9@byu.net>

THANKS

@@ -521,6 +521,7 @@ Thomas Schwinge                     tschwinge@gnu.org
 Thomas Wolff                        mined@towo.net
 Tim J. Robbins                      tjr@FreeBSD.org
 Tim Mooney                          mooney@dogbert.cc.ndsu.NoDak.edu
+Tim Ryan                            Tim_Ryan@bnz.co.nz
 Tim Smithers                        mouse@dmouse.com.au
 Tim Waugh                           twaugh@redhat
 Toby Peterson                       toby@opendarwin.org

src/sort.c

@@ -362,7 +362,8 @@ Other options:\n\
                             NUL-terminated names in file F\n\
 "), stdout);
       fputs (_("\
-  -k, --key=POS1[,POS2]     start a key at POS1, end it at POS2 (origin 1)\n\
+  -k, --key=POS1[,POS2]     start a key at POS1 (origin 1), end it at POS2\n\
+                            (default end of line)\n\
   -m, --merge               merge already sorted files; do not sort\n\
 "), stdout);
       fputs (_("\