added info to changelog

Author: lezwon

CHANGELOG.md

@@ -18,6 +18,8 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/).
 
 - Early stopping checks `on_validation_end` ([#1458](https://github.com/PyTorchLightning/pytorch-lightning/pull/1458))
 
+- Speed up single core TPU training by loading data using `ParallelLoader`.  ([#2033](https://github.com/PyTorchLightning/pytorch-lightning/pull/2033))
+
 ### Changed
 
 - Allow user to select individual TPU core to train on ([#1729](https://github.com/PyTorchLightning/pytorch-lightning/pull/1729))