cubicweb #3171971 cubes README not included in debian package [validation pending]

Skeleton could be updated to fix this.

prioritynormal
typebug
done in3.17.10
load0.500
load left0.000
closed by#05aaa94c04f2 [skeleton] Install cubes README in Debian packages (Closes #3171971)
patch[skeleton] Install cubes README in Debian packages (Closes #3171971) [applied]