perf report/top: Add a tip about system-wide collection from all CPUs

Signed-off-by: Donghyun Kim <[e-mail]>
Cc: Jiri Olsa <[e-mail]>
Cc: Namhyung Kim <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: Taeung Song <[e-mail]>
Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/perf/Documentation/tips.txt

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 If you prefer Intel style assembly, try: perf annotate -M intel
 For hierarchical output, try: perf report --hierarchy
 Order by the overhead of source file name and line number: perf report -s srcline
+System-wide collection from all CPUs: perf record -a