docs: clarify that setting MAXTEXT_CKPT_PATH is required in Option 2

The word "can" made the step sound optional, but the env var is required
for the training command to succeed. Align phrasing with Option 1.

Author: Shuwen-Fang

docs/tutorials/posttraining/rl.md

@@ -98,7 +98,7 @@ export MAXTEXT_CKPT_PATH=<CKPT_PATH> # e.g., gs://my-bucket/my-model-checkpoint/
 
 ### Option 2: Converting from a Hugging Face checkpoint
 
-Refer the steps in [Hugging Face to MaxText](../../guides/checkpointing_solutions/convert_checkpoint.md#hugging-face-to-maxtext) to convert a hugging face checkpoint to MaxText. Make sure you have correct checkpoint files converted and saved. Similar as Option 1, you can set the following environment and move on.
+Refer the steps in [Hugging Face to MaxText](../../guides/checkpointing_solutions/convert_checkpoint.md#hugging-face-to-maxtext) to convert a hugging face checkpoint to MaxText. Make sure you have correct checkpoint files converted and saved. Similar to Option 1, set the following environment variable and move on to the next section.
 
 ```bash
 export MAXTEXT_CKPT_PATH=<CKPT_PATH> # e.g., gs://my-bucket/my-model-checkpoint/0/items