fix: use proj.device instead of hardcoded cuda, fix README typos

- Replace hardcoded device="cuda" with proj.device in SIGReg for
  portability (e.g. macOS MPS, CPU)
- Fix "Both functions accept" → "This function accepts" (only one
  function is shown)
- Fix "please reference in your paper" → "please reference it in
  your paper"

README.md

@@ -16,7 +16,7 @@
   <img src="assets/lewm.gif" width="80%">
 </p>
 
-If you find this code useful, please reference in your paper:
+If you find this code useful, please reference it in your paper:
 ```
 @article{maes_lelidec2026lewm,
   title={LeWorldModel: Stable End-to-End Joint-Embedding Predictive Architecture from Pixels},
@@ -117,7 +117,7 @@ import stable_worldmodel as swm
 cost = swm.policy.AutoCostModel('pusht/lewm')
 ```
 
-Both functions accept:
+This function accepts:
 - `run_name` — checkpoint path **relative to `$STABLEWM_HOME`**, without the `_object.ckpt` suffix
 - `cache_dir` — optional override for the checkpoint root (defaults to `$STABLEWM_HOME`)