Set discrete action tokenizer repo

Replace the discrete action tokenizer placeholder with allenai/MolmoAct2-FAST-Tokenizer.

README.md

@@ -149,7 +149,7 @@ Discrete action inference requires a caller-provided action tokenizer. It is not
 
 ```python
 action_tokenizer = AutoProcessor.from_pretrained(
-    "YOUR_ACTION_TOKENIZER_REPO",
+    "allenai/MolmoAct2-FAST-Tokenizer",
     trust_remote_code=True,
 )