docs: fix Muse README to include approve and correct install path

README previously showed muse plugins install ./.muse-plugin and
muse marketplace add (missing plugins prefix) and omitted the required
hooks approval step. Muse warns "hooks require review before
activation" on install; fix to muse plugins install ./ + muse plugins
approve superpowers per installed flow validated with muse-spark-1.3.

Co-Authored-By: Muse Spark

README.md

@@ -284,13 +284,11 @@ Superpowers is available as a native Muse plugin — same repo, same skills, all
 Install from this repository:
 
 ```bash
-muse plugins install ./.muse-plugin
-# or from a marketplace snapshot
-muse marketplace add superpowers ./.muse-plugin
-muse plugins install superpowers@superpowers-dev
+muse plugins install ./
+muse plugins approve superpowers
 ```
 
-The plugin registers all 16 skills and the `SessionStart` bootstrap hook — `using-superpowers` is injected automatically every session with no per-session opt-in, alongside Claude Code, Codex, Cursor, Gemini, Pi, and the rest. Version is tracked in `.version-bump.json` so `scripts/bump-version.sh` keeps it in sync.
+The plugin registers all 16 skills and the `SessionStart` bootstrap hook — `using-superpowers` is injected automatically every session with no per-session opt-in, alongside Claude Code, Codex, Cursor, Gemini, Pi, and the rest. Hooks require approval on first install. Version is tracked in `.version-bump.json` so `scripts/bump-version.sh` keeps it in sync.
 
 ## The Basic Workflow