Add help sections in the Administration of XWiki

Currently, half of the Administration section document is used : 50% of the area.
Moreover, several users, after a quick review of the Administration, are lost and don't know how to configure some options.

The improvement suggested consists on adding a help section of the right side of the area. It would describe what are the options/properties on this section, how to fill it, what they are used for, etc.