evals: drop SUPERPOWERS_ROOT setup step from README/CLAUDE

The cli.py helper now defaults the env var. Mention as override only.

evals/CLAUDE.md

@@ -40,6 +40,7 @@ Superpowers skill compliance benchmark. Python 3.11+, managed with uv.
 ## Required env
 
 ```
-SUPERPOWERS_ROOT=/path/to/superpowers
 ANTHROPIC_API_KEY=sk-...
 ```
+
+`SUPERPOWERS_ROOT` defaults to the parent of `evals/` (the superpowers repo root). Override only if running drill against a different superpowers checkout.

evals/README.md

@@ -20,10 +20,11 @@ uv sync --dev
 
 Required environment:
 ```bash
-export SUPERPOWERS_ROOT=/path/to/superpowers
 export ANTHROPIC_API_KEY=sk-...
 ```
 
+`SUPERPOWERS_ROOT` defaults to the parent of `evals/` (the superpowers repo root) and only needs to be set if you're running drill against a different superpowers checkout.
+
 ## Usage
 
 ```bash