Documentation on creating base images is in both the Wiki and the CMS:
The docs should be consolidated into a single place. Since it is part of getting an install set up, it should probably be in the CMS. However, the docs are currently more complete in the Wiki. If things are left in the Wiki, the docs in the CMS should be removed and the docs in the Wiki should be linked to from the bottom of the 2.4 Install Guide:
under Initial Administration Steps After Installing VCL (#2).