Clarify installation instructions (#34)
Clarify installation instructions (#34)

1. Fix flow: first install, then add path/script, then check current size, then add limit, then add to CI.
2. Explain what to should be in the `path` option.
3. Don’t use npx, we already have a local package by this time.
4. Improve consistency a bit.

Closes #33
ai/size-limit,ai/size-limit