Lowercase birefnet in model card metadata (#3)

- Lowercase birefnet in model card metadata (5bd48e8cad20182433d3ce9da6dc085b963ce788)


Co-authored-by: Lucain Pouget <[email protected]>

README.md

@@ -1,5 +1,5 @@
 ---
-library_name: BiRefNet
+library_name: birefnet
 tags:
 - background-removal
 - mask-generation