memory-barriers.txt: Sort wait_event* and wait_on_bit* list alphabetically

Commit 8817270 ("docs/memory-barriers.txt: Add wait_event_cmd()
and wait_event_exclusive_cmd()") added two APIs without taking care
of the list order.  Sort the list for readability.

While there, make it clear that this is incomplete by saying
"for example".

Signed-off-by: Akira Yokosawa <akiyks@gmail.com>
Reviewed-by: Håkon Bugge <haakon.bugge@oracle.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

Author: akiyks

Documentation/memory-barriers.txt

@@ -2182,18 +2182,18 @@ set_current_state() may be wrapped by:
 
 which therefore also imply a general memory barrier after setting the state.
 The whole sequence above is available in various canned forms, all of which
-interpolate the memory barrier in the right place:
+interpolate the memory barrier in the right place, for example:
 
 	wait_event();
+	wait_event_cmd();
+	wait_event_exclusive_cmd();
 	wait_event_interruptible();
 	wait_event_interruptible_exclusive();
 	wait_event_interruptible_timeout();
 	wait_event_killable();
 	wait_event_timeout();
 	wait_on_bit();
 	wait_on_bit_lock();
-	wait_event_cmd();
-	wait_event_exclusive_cmd();
 
 
 Secondly, code that performs a wake up normally follows something like this: