Adding license

README.md

@@ -9,14 +9,16 @@ tags:
 - evaluate
 - metric
 description: >-
-  This is a fork of the huggingface evaluate library's implementation of perplexity. 
-  
+  This is a fork of the huggingface evaluate library's implementation of
+  perplexity. 
+
   Perplexity (PPL) is one of the most common metrics for evaluating language
   models. It is defined as the exponentiated average negative log-likelihood of
   a sequence, calculated with exponent base `e`.
 
   For more information on perplexity, see [this
   tutorial](https://huggingface.co/docs/transformers/perplexity).
+license: apache-2.0
 ---
 
 # Perplexity Metric