Explain how to build before explaining how to publish

There is implied information in the "how to configure the project" section, but there is no concrete explanation on what file does what in the build process and more generally, for instance for standard library dependencies.
There should be a first section that explains all of that.

And I'll add that it's at least as important as the publishing part : I may very well want to make a multiplatform library while not publishing it, or at least not in the way this tutorial shows. Maybe I want to publish the JS part on NPM for example.

Start with the tutorial's existing "how to configure the project" and publishing sections. Document what each relevant file does in the build process, including standard library dependencies, before the publishing guidance; done means a reader can understand how to build a multiplatform library without publishing it.

Written by the indexing model from the issue text.