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: 2055fdaf

 ("perf list: Document precise event sampling for AMD IBS")
Signed-off-by: Kim Phillips <kim.phillips@amd.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Alexey Budankov <alexey.budankov@linux.intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Jin Yao <yao.jin@linux.intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Paul Clarke <pc@us.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Tony Jones <tonyj@suse.de>
Cc: stable@vger.kernel.org
Link: http://lore.kernel.org/lkml/20200901215853.276234-1-kim.phillips@amd.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>