perf config: Add initial man page

Add perf-config document to describe the perf configuration and a
'list’ subcommand.

Signed-off-by: Taeung Song <treeze.taeung@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: http://lkml.kernel.org/r/63AD9B57-7B8C-46F8-8F18-0FFEB9A6A1BC@gmail.com


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>