docs: clarify Yarn 4 (Berry) and Corepack requirements for local development

[Kalpana-chavhan]

Problem

The Fuselage repository uses Yarn 4 (Berry), but this is not clearly stated in the README.

New contributors, especially on Windows, often attempt to run:

• npm install, or
• Yarn Classic (v1)

This leads to confusing errors, failed workspace builds, or broken installs due to the presence of .yarnrc.yml, .yarn/, and Yarn 4–specific behavior.

Why this matters

A failed local setup is often the first interaction a contributor has with the codebase.
Unclear tooling requirements can cause contributors to give up before making their first contribution.

Proposed improvement

• Explicitly state that the repository uses Yarn 4 (Berry).
• Recommend Corepack as the supported way to install and manage Yarn.
• Add a short Windows-specific note about long path issues.
• Clarify that peer dependency warnings during yarn install are often expected in this monorepo.

This would significantly improve contributor onboarding without changing any runtime or production code.