Update links to perf_data_converter

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README.md

 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