Merge pull request #35 from rauls5382/master

Add links to perf_data_converter

README.md

 Type 'help' for available commands/options.
 ```
 
+## Using pprof with Linux Perf
+
+pprof can read `perf.data` files generated by the
+[Linux perf](https://perf.wiki.kernel.org/index.php) tool by using the
+`perf_to_profile` program from the
+(perf\_data\_converter)[http://github.com/google/perf\_data\_converter] package.
+
 ## Further documentation
 
 See doc/pprof.md for more detailed end-user documentation.

internal/driver/fetch.go

 	cmd := exec.Command("perf_to_profile", perfPath, profile.Name())
 	if err := cmd.Run(); err != nil {
 		profile.Close()
-		return nil, err
+		return nil, fmt.Errorf("failed to convert perf.data file. Try github.com/google/perf_data_converter: %v", err)
 	}
 	return profile, nil
 }