Update links to perf_data_converter

As they are they don't get properly rendered.

README.md

@@ -75,7 +75,7 @@ Type 'help' for available commands/options.
 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.
+(perf_data_converter)[http://github.com/google/perf_data_converter] package.
 
 ## Further documentation