perf report: Show random usage tip on the help line

perf report: Show random usage tip on the help line

Currently perf report only shows a help message "For a higher level
overview, try: perf report --sort comm,dso" unconditionally (even if
the sort keys were used).  Add more help tips and show randomly.

Load tips from ${prefix}/share/doc/perf-tip/tips.txt file.

  $ perf report | tail
      0.10%  swapper  [kernel.vmlinux]   [k] irq_exit
      0.09%  swapper  [kernel.vmlinux]   [k] flush_smp_call_function_queue
      0.08%  swapper  [kernel.vmlinux]   [k] native_write_msr_safe
      0.03%  swapper  [kernel.vmlinux]   [k] group_sched_in
      0.01%  perf     [kernel.vmlinux]   [k] native_write_msr_safe

  #
  # (Tip: Search options using a keyword: perf report -h <keyword>)
  #

Signed-off-by: Namhyung Kim <[email protected]>
Acked-by: Ingo Molnar <[email protected]>
Cc: Andi Kleen <[email protected]>
Cc: David Ahern <[email protected]>
Cc: Jiri Olsa <[email protected]>
Cc: Masami Hiramatsu <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Stephane Eranian <[email protected]>
Cc: Wang Nan <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
[ Renamed it to perf_tip() and the parameter dirname to dirpath to fix the build on older distros ]
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>