perf top: Document --ignore-vmlinux

We've had this since 2013, document it.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jin Yao <yao.jin@linux.intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Cc: Willy Tarreau <w@1wt.eu>
Fixes: fc2be696 ("perf symbols: Add new option --ignore-vmlinux for perf top")
Link: https://lkml.kernel.org/n/tip-0jwfueooddwfsw9r603belxi@git.kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/Documentation/perf-top.txt

@@ -67,6 +67,9 @@ Default is to monitor all CPUS.
 --vmlinux=<path>::
 	Path to vmlinux.  Required for annotation functionality.
 
+--ignore-vmlinux::
+	Ignore vmlinux files.
+
 -m <pages>::
 --mmap-pages=<pages>::
 	Number of mmap data pages (must be a power of two) or size