perf evsel: Extend message to mention CAP_SYS_PTRACE and perf security doc link

Adjust limited access message to mention CAP_SYS_PTRACE capability for
processes of unprivileged users. Add link to perf security document in
the end of the section about capabilities.

The change has been inspired by this discussion:
https://lore.kernel.org/lkml/20200722113007.GI77866@kernel.org/Signed-off-by: Alexey Budankov <alexey.budankov@linux.intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lore.kernel.org/lkml/6f8a7425-6e7d-19aa-1605-e59836b9e2a6@linux.intel.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/evsel.c

@@ -2502,8 +2502,10 @@ int evsel__open_strerror(struct evsel *evsel, struct target *target,
 
 		return scnprintf(msg + printed, size - printed,
 		 "Consider adjusting /proc/sys/kernel/perf_event_paranoid setting to open\n"
-		 "access to performance monitoring and observability operations for users\n"
-		 "without CAP_PERFMON or CAP_SYS_ADMIN Linux capability.\n"
+		 "access to performance monitoring and observability operations for processes\n"
+		 "without CAP_PERFMON, CAP_SYS_PTRACE or CAP_SYS_ADMIN Linux capability.\n"
+		 "More information can be found at 'Perf events and tool security' document:\n"
+		 "https://www.kernel.org/doc/html/latest/admin-guide/perf-security.html\n"
 		 "perf_event_paranoid setting is %d:\n"
 		 "  -1: Allow use of (almost) all events by all users\n"
 		 "      Ignore mlock limit after perf_event_mlock_kb without CAP_IPC_LOCK\n"