Update pipeline tag

It seems the previous (automated) PRs updated all ppeline tags to "image-to-image".

However, for model repos for which "depth-estimation" is more appropriate, feel free to add it as that seems more appropriate.

README.md

@@ -2,7 +2,7 @@
 language:
 - en
 license: openrail++
-pipeline_tag: image-to-image
+pipeline_tag: depth-estimation
 library_name: diffusers
 tags:
 - depth estimation