perf probe: Add permission and sysctl notice to man page

Add a section to notify the permission and sysctl setting for perf
probe. And fix some indentations.

Reported-by: Ravi Bangoria <ravi.bangoria@linux.ibm.com>
Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Reviewed-by: Ravi Bangoria <ravi.bangoria@linux.ibm.com>
Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Link: http://lore.kernel.org/lkml/162204068898.388434.16842705842611255787.stgit@devnote2


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