docs(website): update pnpm commands

[sachinraja]

Summary

• pnpm deprecated pnpx in favor of pnpm dlx
• pnpm suggests using pnpm add <pkg> in its docs and does not mention pnpm i <pkg> (although it is supported)
• pnpm allows passing through script names like Yarn (pnpm format instead of pnpm run format)

Test Plan

n/a

[ematipico]

That's great! Thank you for making the documentation more up to date!