OpenIXCLab/SeC-4B · Improve model card: Update pipeline tag, add library name, and usage example

This PR enhances the model card for the SeC model by:

Updating the pipeline_tag from mask-generation to image-segmentation for more precise categorization of the Video Object Segmentation task. This will improve discoverability on the Hugging Face Hub.
Adding library_name: transformers to correctly reflect the model's compatibility and usage with the Hugging Face Transformers library, enabling the "Use in Transformers" widget.
Including a basic Python usage example to demonstrate how to load and interact with the model, making it easier for users to get started.

These changes will help users better understand the model's capabilities and how to use it within the Hugging Face ecosystem.