Tree shaking clarification

[yishay-at-bay]

Feature to document
Tree shaking

Author(s)

Additional information
In the tree shaking documentation here there is an example that includes the Shopify project. The example lacks some details about the full structure of the files and is a bit hard to understand. It would be great if you can write more about the logic behind the sideEffect flag and maybe even give a full example of a npm package with some css assets that contain side effects and how it is ignored mistakenly by a consumer app if the sideEffect flag is set to false

[ ] I am willing to work on this issue and submit a pull request.