perf script: add -S/--symbols documentation

Capture both that this option exists and that symbols can be hexadecimal
addresses.
Signed-off-by: Ian Rogers <irogers@google.com>
Suggested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lore.kernel.org/lkml/20200402174130.140319-1-irogers@google.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/Documentation/perf-script.txt

@@ -412,6 +412,14 @@ include::itrace.txt[]
 --xed::
 	Run xed disassembler on output. Requires installing the xed disassembler.
 
+-S::
+--symbols=symbol[,symbol...]::
+	Only consider the listed symbols. Symbols are typically a name
+	but they may also be hexadecimal address.
+
+	For example, to select the symbol noploop or the address 0x4007a0:
+	perf script --symbols=noploop,0x4007a0
+
 --call-trace::
 	Show call stream for intel_pt traces. The CPUs are interleaved, but
 	can be filtered with -C.