Add pipeline tag and library name

This PR adds the `pipeline_tag` and `library_name` to the model card metadata. This improves discoverability of the model and clarifies its usage. The `pipeline_tag` is set to `audio-to-audio` because the model is an acoustic codec tokenizer.

README.md

@@ -1,5 +1,7 @@
 ---
 license: mit
+pipeline_tag: audio-to-audio
+library_name: diffusers
 ---
 
 # WavTokenizer