feat(migrate): Add model card generation and saving to migration script

- Implemented functionality to generate and save a model card for the migrated model, including metadata such as dataset repository ID, license, and tags.
- Enhanced the script to push the model card to the hub if requested, improving model documentation and accessibility.
- Refactored the saving process to ensure the model card is saved locally and uploaded correctly when pushing to the hub.

src/lerobot/processor/migrate_policy_normalization.py

@@ -411,6 +411,7 @@ def main():
         UnnormalizerProcessor(features=output_features, norm_map=norm_map, stats=stats),
     ]
     postprocessor = RobotProcessor(postprocessor_steps, name=f"{policy_type}_postprocessor")
+
     # Determine hub repo ID if pushing to hub
     if args.push_to_hub:
         if args.hub_repo_id:
@@ -424,12 +425,6 @@ def main():
     else:
         hub_repo_id = None
 
-    # Save model using the policy's save_pretrained method
-    print(f"Saving model to {output_dir}...")
-    policy.save_pretrained(
-        output_dir, push_to_hub=args.push_to_hub, repo_id=hub_repo_id, private=args.private
-    )
-
     # Save preprocessor and postprocessor to root directory
     print(f"Saving preprocessor to {output_dir}...")
     preprocessor.save_pretrained(output_dir)
@@ -441,6 +436,44 @@ def main():
     if args.push_to_hub:
         postprocessor.push_to_hub(repo_id=hub_repo_id, private=args.private)
 
+    # Save model using the policy's save_pretrained method
+    print(f"Saving model to {output_dir}...")
+    policy.save_pretrained(
+        output_dir, push_to_hub=args.push_to_hub, repo_id=hub_repo_id, private=args.private
+    )
+
+    # Generate and save model card
+    print("Generating model card...")
+    # Get metadata from original config
+    dataset_repo_id = config.get("repo_id", "unknown")
+    license = config.get("license", "apache-2.0")
+
+    tags = config.get("tags", ["robotics", "lerobot", policy_type]) or ["robotics", "lerobot", policy_type]
+    tags = set(tags).union({"robotics", "lerobot", policy_type})
+    tags = list(tags)
+
+    # Generate model card
+    card = policy.generate_model_card(
+        dataset_repo_id=dataset_repo_id, model_type=policy_type, license=license, tags=tags
+    )
+
+    # Save model card locally
+    card.save(str(output_dir / "README.md"))
+    print(f"Model card saved to {output_dir / 'README.md'}")
+    # Push model card to hub if requested
+    if args.push_to_hub:
+        from huggingface_hub import HfApi
+
+        api = HfApi()
+        api.upload_file(
+            path_or_fileobj=str(output_dir / "README.md"),
+            path_in_repo="README.md",
+            repo_id=hub_repo_id,
+            repo_type="model",
+            commit_message="Add model card for migrated model",
+        )
+        print("Model card pushed to hub")
+
     print("\nMigration complete!")
     print(f"Migrated model saved to: {output_dir}")
     if args.push_to_hub: