Link the model card to the model it was fine-tuned from

Sets `base_model: robometer/Robometer-4B` in the model card metadata, so this model shows up in its parent's model tree on the Hub. The parent comes from the `pretrained_path` recorded in this checkpoint's `config.json` (`robometer/Robometer-4B`).

README.md

@@ -12,6 +12,7 @@ tags:
 - zero-shot
 - robometer
 - vision-language
+base_model: robometer/Robometer-4B
 ---
 
 # Reward Model Card for robometer