perf timechart: Add example in the documentation

While at it, update the synopsis to show both forms.

Signed-off-by: Ramkumar Ramachandra <[e-mail]>
Cc: David Ahern <[e-mail]>
Cc: Ingo Molnar <[e-mail]>
Cc: Namhyung Kim <[e-mail]>
Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/perf/Documentation/perf-timechart.txt

···
 SYNOPSIS
 --------
 [verse]
-'perf timechart' {record}
+'perf timechart' record <command>
+'perf timechart' [<options>]
 
 DESCRIPTION
 -----------
···
 
 --symfs=<directory>::
         Look for files with symbols relative to this directory.
+
+EXAMPLES
+--------
+
+$ perf timechart record git pull
+
+  [ perf record: Woken up 13 times to write data ]
+  [ perf record: Captured and wrote 4.253 MB perf.data (~185801 samples) ]
+
+$ perf timechart
+
+  Written 10.2 seconds of trace to output.svg.
 
 SEE ALSO
 --------