[tde-team-gentoo] Conditional build of documentation in the core package

Hi Gentoo team, when revising TDE/tdegames#11, which adds conditions so that only the documentation for applications that are built is installed, I realized that I don't know how you build the documentation for the core packages and whether this will cause a problem for your packaging? Please can you look at it? See https://mirror.git.trinitydesktop.org/gitea/TDE/tdegames/pulls/11 The idea seems good to me and I assume that it could be used for other core modules in the same way. Cheers -- Slávek