Add "text-to-3D" pipeline tag

This PR ensures people can find your model at https://huggingface.co/models?pipeline_tag=text-to-3d&sort=trending

README.md

@@ -1,3 +1,7 @@
+---
+pipeline_tag: text-to-3d
+---
+
 <div align="center">
 
 <h1>