Update pipeline tag

This PR ensures the model can be found at https://huggingface.co/models?pipeline_tag=image-text-to-text&sort=trending.

README.md

@@ -1,5 +1,6 @@
 ---
 license: apache-2.0
+pipeline_tag: image-text-to-text
 tags:
 - MobileVLM V2
 ---