docs(readme): clarify yarn workspace usage

[UserSbondorf]

Summary

Add a short note under the local development example to clarify that Yarn workspace commands should be run from the repository root.

Motivation

This helps contributors avoid workspace resolution errors when starting the web app locally.

[cb-heimdall]

🟡 Heimdall Review Status

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Reviews	🟡 0/1	Denominator calculation Show calculation 1 if user is bot 0 1 if user is external 0 2 if repo is sensitive 0 From .codeflow.yml 1 Additional review requirements Show calculation Max 0 0 From CODEOWNERS 0 Global minimum 0 Max 1 1 1 if commit is unverified 0 Sum 1

[vercel]

@UserSbondorf is attempting to deploy a commit to the Coinbase Team on Vercel.

A member of the Team first needs to authorize it.