add provision warning

.claude/skills/hf-space-sandbox/SKILL.md

@@ -13,6 +13,14 @@ Run scripts on remote sandbox hardware via SSH.
 uv run scripts/sandbox.py create user/sandbox
 ```
 
+## Check Status
+
+Before SSHing, check the status of the sandbox to ensure it is ready. It may take a few minutes to provision.
+
+```bash
+uv run scripts/sandbox.py status user/sandbox
+```
+
 ## SSH Access
 
 ```bash