docs: add workspace dependencies example to workspaces

[MaxBlack-dev]

Description

Adds documentation and examples showing how to add one workspace as a dependency of another workspace using the workspace protocol.

Changes

• Added a new section explaining how to use workspace:* protocol to add workspace dependencies
• Included example command: npm install b@workspace:* -w a
• Showed the resulting package.json entry
• Explained that workspace: protocol links to local workspace instead of registry

Fixes

Closes #4742

Rationale

The workspaces documentation explained how to add registry dependencies to workspaces, but did not explain how to add one workspace as a dependency of another workspace. This is a common use case in monorepos where internal packages depend on each other.

Type of Change

Documentation enhancement