Add description to card metadata

README.md

@@ -1,6 +1,6 @@
 ---
 title: Mean IoU
-emoji: 🤗 
+emoji: 🤗
 colorFrom: blue
 colorTo: red
 sdk: gradio
@@ -8,10 +8,18 @@ sdk_version: 3.0.2
 app_file: app.py
 pinned: false
 tags:
-- evaluate
-- metric
----
+  - evaluate
+  - metric
+description: >-
+  IoU is the area of overlap between the predicted segmentation and the ground
+  truth divided by the area of union
+
+  between the predicted segmentation and the ground truth. For binary (two
+  classes) or multi-class segmentation,
 
+  the mean IoU of the image is calculated by taking the IoU of each class and
+  averaging them.
+---
 # Metric Card for Mean IoU