Update Weave Models Integration tutorial with Registry backlink (#1238)

## Description of the change

Updating the docs with changes to have the Registry backlink generate in
Weave

The Colab linked already has the code changes, wanted to get this
tutorial in line with the Colab changes

---------

Co-authored-by: Matt Linville <matt.linville@wandb.com>

Author: knisar

content/tutorials/weave_models_registry.md

@@ -84,9 +84,9 @@ class UnslothLoRAChatModel(weave.Model):
     _tokenizer: Any = PrivateAttr()
 
     def model_post_init(self, __context):
-        # paste this from the "Use" tab from the registry
         run = wandb.init(project=PROJECT, job_type="model_download")
-        artifact = run.use_artifact(f"{self.chat_model}")
+        artifact_ref = self.chat_model.replace("wandb-artifact:///", "")
+        artifact = run.use_artifact(artifact_ref)
         model_path = artifact.download()
 
         # unsloth version (enable native 2x faster inference)
@@ -126,7 +126,9 @@ class UnslothLoRAChatModel(weave.Model):
 Now create a new model with a specific link from the registry:
 
 ```python
-MODEL_REG_URL = "wandb32/wandb-registry-RAG Chat Models/Finetuned Llama-3.2:v3"
+ORG_ENTITY = "wandb32"  # replace this with your organization name
+artifact_name = "Finetuned Llama-3.2" # replace this with your artifact name
+MODEL_REG_URL = f"wandb-artifact:///{ORG_ENTITY}/wandb-registry-RAG Chat Models/{artifact_name}:v3"
 
 max_seq_length = 2048
 dtype = None