Add `library_name: transformers` to metadata

This PR improves the model card for `cyberagent/layerd-birefnet` by adding `library_name: transformers` to the metadata.

This addition is supported by the `config.json` and the existing "Usage" section, which demonstrates how to load the model using `transformers.AutoModelForImageSegmentation`. Adding this metadata enables the automated "How to use" widget on the Hugging Face Hub, making it easier for users to get started with the model.

No changes were made to the paper links in the content, as the existing Arxiv links are sufficient and align with the guidelines.

README.md

@@ -1,12 +1,13 @@
 ---
-license: apache-2.0
 language: en
-tags:
-  - layer decomposition
-  - image segmentation
-  - image matting
-  - design
+license: apache-2.0
 pipeline_tag: image-segmentation
+library_name: transformers
+tags:
+- layer decomposition
+- image segmentation
+- image matting
+- design
 ---
 
 ## LayerD BiRefNet Matting Module