* docs: update the ROOT documentation and error messages
* The documentation now reflects what happens in the
setting/repository.go::newRepository function:
filepath.Join(AppWorkPath, RepoRootPath) was missing.
* The error message displayed when RepoRootPath is not found now
displays the value of RepoRootPath. Given the complexity of the
construction of this value, only referring to it in the abstract
is likely to be misleading to the Gitea admin trying to interpret
the message.
Co-authored-by: delvh <dev.lh@web.de>