[docs] create a page for working with non npm dependencies

[bestander]

https://yarnpkg.com/en/docs/dependencies

• git hosted
• alternative names "dep-a": "npm:dep-b@1.0.0"
• link: specifier
• file: specifier + yarn-link-file-dependencies config
• workspaces
• configuring proxy and registry via .yarnrc/npmrc