Correct pipeline tag

This PR fixes the pipeline tag (sorry previous one was wrong).

README.md

@@ -2,7 +2,7 @@
 language:
 - en
 license: cc-by-nc-4.0
-pipeline_tag: image-text-to-text
+pipeline_tag: zero-shot-image-classification
 library_name: transformers
 tags:
 - medical