Update contributing.md to link to walkthrough video. (#34299)
Update contributing.md to link to walkthrough video. (#34299)

Hopefully this helps folks contribute 😄 
azukaru/next.js,JeromeFitz/next.js,azukaru/next.js,azukaru/next.js,JeromeFitz/next.js,JeromeFitz/next.js,azukaru/next.js,JeromeFitz/next.js