Add pipeline tag

This PR adds the `pipeline_tag` metadata to ensure the model can be found via the image-segmentation pipeline filter on the Hub.

README.md

@@ -1,11 +1,12 @@
 ---
 license: cc-by-4.0
+pipeline_tag: image-segmentation
 tags:
-  - single-pixel-imaging
-  - image-free-inference
-  - segmentation
-  - computational-imaging
-  - pytorch
+- single-pixel-imaging
+- image-free-inference
+- segmentation
+- computational-imaging
+- pytorch
 ---
 
 # STSF+TPLS — pretrained checkpoints