Add description to card metadata

SacreBLEU provides hassle-free computation of shareable, comparable, and reproducible BLEU scores.
Inspired by Rico Sennrich's `multi-bleu-detok.perl`, it produces the official WMT scores but works with plain text.
It also knows all the standard test sets and handles downloading, processing, and tokenization for you.

See the [README.md] file at https://github.com/mjpost/sacreBLEU for more information.

README.md

@@ -1,6 +1,6 @@
 ---
 title: SacreBLEU
-emoji: 🤗 
+emoji: 🤗
 colorFrom: blue
 colorTo: red
 sdk: gradio
@@ -8,10 +8,22 @@ sdk_version: 3.0.2
 app_file: app.py
 pinned: false
 tags:
-- evaluate
-- metric
----
+  - evaluate
+  - metric
+description: >-
+  SacreBLEU provides hassle-free computation of shareable, comparable, and
+  reproducible BLEU scores.
+
+  Inspired by Rico Sennrich's `multi-bleu-detok.perl`, it produces the official
+  WMT scores but works with plain text.
+
+  It also knows all the standard test sets and handles downloading, processing,
+  and tokenization for you.
 
+
+  See the [README.md] file at https://github.com/mjpost/sacreBLEU for more
+  information.
+---
 # Metric Card for SacreBLEU