chore: update README to select single gpu

Author: fin-griffin

sweep/README.md

@@ -32,7 +32,7 @@ wandb login
 
 ```bash
 cd sweep
-python sweep.py --dry-run
+CUDA_VISIBLE_DEVICES=3 python sweep.py --dry-run
 ```
 
 ## Running the sweep
@@ -42,7 +42,7 @@ Start a tmux session so the sweep survives SSH disconnection:
 ```bash
 tmux new -s sweep
 cd sweep
-python sweep.py
+CUDA_VISIBLE_DEVICES=3 python sweep.py
 # Ctrl+B, D  →  detach (safe to close laptop)
 # tmux attach -t sweep  →  reconnect later
 ```
@@ -55,7 +55,7 @@ Progress is logged to `sweep.log` and to the W&B project `VOICE`.
 it will skip completed runs and retry failed ones:
 
 ```bash
-python sweep.py
+CUDA_VISIBLE_DEVICES=3 python sweep.py
 ```
 
 ## Outputs