update CONTRIBUTING.md

[PawelJastrzebski]

I'm not sure about npm run watch:front-end this seems to be outdated as such npm script does not exist.

[vercel[bot]]

@PawelJastrzebski is attempting to deploy a commit to the Quadratic Team on Vercel.

A member of the Team first needs to authorize it.

[davidkircos]

Hey @PawelJastrzebski there are lots of updates to the dev process in the branch a-team

Holding off on this until we merge #718