Update contribute page

[lauracumming]

Update text, links and images

[lauracumming]

• [x] Check Cookie banner: banner loads, categories in the right order, cookies disabled by default
  • [x] Check Rapid Router: game loads, can solve a level, can save a workspace, can create a level, can save a level, scores get saved, scoreboard loads
  • [x] Check OS on browserstack
  • [x] Approved on production