perf record/stat: Explicitly call out event modifiers in the documentation

Event modifiers are not mentioned in the perf record or perf stat
manpages. Add them to orient new users more effectively by pointing
them to the perf list manpage for details.

Fixes: 2055fdaf8703 ("perf list: Document precise event sampling for AMD IBS")
Signed-off-by: Kim Phillips <[e-mail]>
Cc: Adrian Hunter <[e-mail]>
Cc: Alexander Shishkin <[e-mail]>
Cc: Alexey Budankov <[e-mail]>
Cc: Ian Rogers <[e-mail]>
Cc: Jin Yao <[e-mail]>
Cc: Jiri Olsa <[e-mail]>
Cc: Mark Rutland <[e-mail]>
Cc: Namhyung Kim <[e-mail]>
Cc: Paul Clarke <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: Stephane Eranian <[e-mail]>
Cc: Tony Jones <[e-mail]>
Cc: [e-mail]
Link: http://lore.kernel.org/lkml/[e-mail]
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/perf/Documentation/perf-record.txt

···
         - a raw PMU event (eventsel+umask) in the form of rNNN where NNN is a
 	  hexadecimal event descriptor.
 
+        - a symbolic or raw PMU event followed by an optional colon
+	  and a list of event modifiers, e.g., cpu-cycles:p.  See the
+	  linkperf:perf-list[1] man page for details on event modifiers.
+
 	- a symbolically formed PMU event like 'pmu/param1=0x3,param2/' where
 	  'param1', 'param2', etc are defined as formats for the PMU in
 	  /sys/bus/event_source/devices/<pmu>/format/*.

tools/perf/Documentation/perf-stat.txt

···
 	- a raw PMU event (eventsel+umask) in the form of rNNN where NNN is a
 	  hexadecimal event descriptor.
 
+        - a symbolic or raw PMU event followed by an optional colon
+	  and a list of event modifiers, e.g., cpu-cycles:p.  See the
+	  linkperf:perf-list[1] man page for details on event modifiers.
+
 	- a symbolically formed event like 'pmu/param1=0x3,param2/' where
 	  param1 and param2 are defined as formats for the PMU in
 	  /sys/bus/event_source/devices/<pmu>/format/*