perf: Document the new transaction sample type

Commit fdfbbd07 ("perf: Add generic transaction flags")
added support for PERF_SAMPLE_TRANSACTION but forgot to add documentation
for the sample type to include/uapi/linux/perf_event.h
Signed-off-by: Vince Weaver <vincent.weaver@maine.edu>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: Andi Kleen <ak@linux.intel.com>
Link: http://lkml.kernel.org/r/alpine.DEB.2.02.1312131548450.10372@pianoman.cluster.toySigned-off-by: Ingo Molnar <mingo@kernel.org>

include/uapi/linux/perf_event.h

@@ -679,6 +679,7 @@ enum perf_event_type {
 	 *
 	 *	{ u64			weight;   } && PERF_SAMPLE_WEIGHT
 	 *	{ u64			data_src; } && PERF_SAMPLE_DATA_SRC
+	 *	{ u64			transaction; } && PERF_SAMPLE_TRANSACTION
 	 * };
 	 */
 	PERF_RECORD_SAMPLE			= 9,