fixup! docs: document release bump levels and the prerelease identifier

Author: not-matthias

CONTRIBUTING.md

@@ -30,7 +30,7 @@ The identifier becomes the npm dist-tag, so a prerelease is installed only by
 asking for it:
 
 ```bash
-npm install @codspeed/vitest-plugin@beta
+pnpm add @codspeed/vitest-plugin@beta
 ```
 
 `latest` keeps pointing at the most recent stable release, and `^5` never