Add 'autogenerated' notice to user_remotes.yml

orchestra/model/configuration.py

@@ -252,6 +252,8 @@ class Configuration:
 
         with open(remotes_config_file, "w") as f:
             f.write(dedent(f"""
+            #! This file was automatically generated by orchestra.
+            #! Edit it to use additional remotes.
             #@data/values
             ---
             #@overlay/match missing_ok=True