Ensure download stats work

This PR adds the `library_name` tag, which will allow to track download stats (I'll open a PR on huggingface.js similar to https://github.com/huggingface/huggingface.js/pull/782).

More context: https://huggingface.co/docs/hub/models-download-stats

README.md

@@ -1,4 +1,5 @@
 ---
 license: apache-2.0
+library_name: animatediff
 ---
 This model repo is for [AnimateDiff](https://github.com/guoyww/animatediff/).