perf record: Amend option summaries

Because there's too many options and I cannot read, I frequently get
confused between -c and -P, and try to do things like:

  perf record -P 50000 -- foo

Which does not work; try and make the option description slightly longer
and hopefully less confusing.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20150610144850.GP19282@twins.programming.kicks-ass.net
[ Do those changes on the man page as well ]
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
diff --git a/tools/perf/Documentation/perf-record.txt b/tools/perf/Documentation/perf-record.txt
index 280533e..6fdf786 100644
--- a/tools/perf/Documentation/perf-record.txt
+++ b/tools/perf/Documentation/perf-record.txt
@@ -152,12 +152,16 @@
 
 -d::
 --data::
-	Sample addresses.
+	Record the sample addresses.
 
 -T::
 --timestamp::
-	Sample timestamps. Use it with 'perf report -D' to see the timestamps,
-	for instance.
+	Record the sample timestamps. Use it with 'perf report -D' to see the
+	timestamps, for instance.
+
+-P::
+--period::
+	Record the sample period.
 
 -n::
 --no-samples::