perf list: Fix documentation of :ppp

Correctly document what is implemented for :ppp on Intel CPUs in recent
kernels.

Signed-off-by: Andi Kleen <ak@linux.intel.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1458575793-12091-2-git-send-email-andi@firstfloor.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/Documentation/perf-list.txt

@@ -40,10 +40,12 @@ address should be. The 'p' modifier can be specified multiple times:
  0 - SAMPLE_IP can have arbitrary skid
  1 - SAMPLE_IP must have constant skid
  2 - SAMPLE_IP requested to have 0 skid
- 3 - SAMPLE_IP must have 0 skid
+ 3 - SAMPLE_IP must have 0 skid, or uses randomization to avoid
+     sample shadowing effects.
 
 For Intel systems precise event sampling is implemented with PEBS
-which supports up to precise-level 2.
+which supports up to precise-level 2, and precise level 3 for
+some special cases
 
 On AMD systems it is implemented using IBS (up to precise-level 2).
 The precise modifier works with event types 0x76 (cpu-cycles, CPU