Add description to card metadata

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.

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(++)