[Qbs] Suggested way to add non-default build variants

[Epting, Thomas]

> What is the suggested way to add non-default build variants in Qbs?
>
> Example: In addition to debug and release, we want to support a
> build variant releaseWithDebugInfo.
>
> The documentation (language-introduction.html) states "By default,
> "debug" and "release" are valid values but the user can add more in
> a project file.", but there is no information how this can actually be
> done.

Maybe there is any more documentation? Some examples?

Thanks,
Thomas