Update backend plugin tutorial to refer to /todos endpoint instead of /health

This PR updates the backend plugin tutorial documentation to match the current plugin template.
Previously, the tutorial referenced a /health endpoint, which does not exist in the generated backend plugin.

Signed-off-by: Ayush More <ayushmore42595@gmail.com>

docs/plugins/backend-plugin.md

@@ -48,11 +48,18 @@ This will think for a bit, and then say `Listening on :7007`. In a different
 terminal window, now run
 
 ```sh
-curl localhost:7007/api/carmen/health
+curl localhost:7007/api/carmen/todos
 ```
 
-This should return `{"status":"ok"}`. Success! Press `Ctrl + c` to stop it
-again.
+You should see the following response:
+```sh
+{
+"items": []
+} 
+```
+:::note Note: The route shown here matches the default in the current backend plugin template. If you want a `/health` endpoint for health checks, you can add it to your router yourself.
+
+:::
 
 ## Developing your Backend Plugin