Add metadata tags

This PR:

- adds the appropriate pipeline tag, so that people can find it at https://huggingface.co./models?pipeline_tag=image-text-to-text
- add the appropriate library name

Cheers!

README.md

@@ -1,5 +1,7 @@
 ---
 license: mit
+library_name: transformers
+pipeline_tag: image-text-to-text
 ---
 ![header](./assets/header.png)