perf list: Add missing documentation for --desc and --debug options

Add missing documentation for --desc and --debug options to the 'perf
list' man page.

Signed-off-by: Sangwon Hong <qpakzk@gmail.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: http://lkml.kernel.org/r/20180717110738.10779-1-qpakzk@gmail.com


[ Clarify that --desc is by default active ]
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>