Add description to card metadata

README.md

@@ -1,6 +1,6 @@
 ---
 title: chrF
-emoji: 🤗 
+emoji: 🤗
 colorFrom: blue
 colorTo: red
 sdk: gradio
@@ -8,10 +8,31 @@ sdk_version: 3.0.2
 app_file: app.py
 pinned: false
 tags:
-- evaluate
-- metric
----
+  - evaluate
+  - metric
+description: >-
+  ChrF and ChrF++ are two MT evaluation metrics. They both use the F-score
+  statistic for character n-gram matches,
+
+  and ChrF++ adds word n-grams as well which correlates more strongly with
+  direct assessment. We use the implementation
+
+  that is already present in sacrebleu.
+
+
+  The implementation here is slightly different from sacrebleu in terms of the
+  required input format. The length of
 
+  the references and hypotheses lists need to be the same, so you may need to
+  transpose your references compared to
+
+  sacrebleu's required input format. See
+  https://github.com/huggingface/datasets/issues/3154#issuecomment-950746534
+
+
+  See the README.md file at https://github.com/mjpost/sacreBLEU#chrf--chrf for
+  more information.
+---
 # Metric Card for chrF(++)