Now, when you start a new react accelerator project. The backoffice part no longer contains the "Litium.Accelerator.Administration.Extensions" project or the "Litium.Accelerator.FieldTypes" project which was a great starting point when adding own fields or panels. The guides on Docs for building fields/panels assume these projects exist.
It is of course possible to install an empty MVC-accelerator, grab the projects and add them to react-accelerator project, which is what i did. Maybe that should not be the future way to do it.
A new guide/starter-kit is needed when starting from empty storefront-project on how to add fields/backoffice panels.