Update README.md for examples/with-mqtt-js

[CachorroC]

changed the "yarn/npm create-next-app" for "yarn/npm create next-app"

Bug

• Related issues linked using fixes #number
• Integration tests added
• Errors have a helpful link attached, see contributing.md

Feature

• Implements an existing feature request or RFC. Make sure the feature request has been accepted for implementation before opening a PR.
• Related issues linked using fixes #number
• e2e tests added
• Documentation added
• Telemetry added. In case of a feature if it's used or not.
• Errors have a helpful link attached, see contributing.md

Documentation / Examples

• Make sure the linting passes by running pnpm build && pnpm lint
• The "examples guidelines" are followed from our contributing doc

[ijjk]

Good catch, thanks!