PerfProfiler: Add hint how to make perf work

Change-Id: I9cef8826163a7f716717470e5b7edfd13699f75c
Reviewed-by: hjk <hjk@qt.io>
Reviewed-by: Ulf Hermann <ulf.hermann@qt.io>
Reviewed-by: Leena Miettinen <riitta-leena.miettinen@qt.io>

src/plugins/perfprofiler/perfprofilertool.cpp

@@ -421,7 +421,8 @@ void PerfProfilerTool::onReaderFinished()
                              tr("The profiler did not produce any samples. "
                                 "Make sure that you are running a recent Linux kernel and that "
                                 "the \"perf\" utility is available and generates useful call "
-                                "graphs."));
+                                "graphs.\nYou might find further explanations in the Application "
+                                "Output view."));
         clear();
     } else {
         m_traceManager->finalize();