Update README.md

Author: AdeelH

README.md

@@ -2,7 +2,7 @@
 
 # Multi-class Focal Loss
 
-An implementation of Focal Loss, as described in the RetinaNet paper, https://arxiv.org/abs/1708.02002, generalized to the multi-class case.
+An (unofficial) implementation of Focal Loss, as described in the RetinaNet paper, https://arxiv.org/abs/1708.02002, generalized to the multi-class case.
 
 It is essentially an enhancement to cross-entropy loss and is useful for classification tasks when there is a large class imbalance. It has the effect of underweighting easy examples.