Add pipeline tag, link to paper

This PR makes sure people can find the model at https://huggingface.co/papers/2409.11340, and at https://huggingface.co/models?pipeline_tag=text-to-image&sort=trending.

README.md

@@ -1,3 +1,17 @@
----
-license: mit
----
+---
+license: mit
+pipeline_tag: text-to-image
+tags:
+- image-to-image
+---
+
+This repository contains the model of the paper [OmniGen: Unified Image Generation](https://huggingface.co/papers/2409.11340).
+
+## OmniGen
+
+OmniGen is a unified image generation model that you can use to perform various tasks, including but not limited to text-to-image generation,
+subject-driven generation, Identity-Preserving Generation, image editing, and image-conditioned generation.
+OmniGen don't need additional plugins or operations, it can automatically identify the features (e.g., required object, human pose, depth mapping)
+in input images according the text prompt. 
+
+Code: https://github.com/VectorSpaceLab/OmniGen