perf config: Document variables for 'annotate' section in man page

Explain 'annotate' section and its variables.

'hide_src_code', 'use_offset', 'jump_arrows',
'show_linenr', 'show_nr_jump' and 'show_total_period'.

Signed-off-by: Taeung Song <treeze.taeung@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: http://lkml.kernel.org/r/1452253193-30502-5-git-send-email-treeze.taeung@gmail.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>