[horde] Documentation on Horde/composer

[Ralf Lang]

Hello,

install docs for Horde from Composer are in progress.
https://wiki.horde.org/Doc/Dev/H6/Installation

As each installation out there in the wild is different, I follow an 
iterative approach:

- How to get the base system up and running with users from the SQL 
database.
- How to install the specific apps, starting from trivial (nag, mnemo, 
kronolith) to more complex (turba, imp, ingo)
- How to maintain an existing installation
- What to backup

If you already have your config files and database content, a more 
concise restore article is proposed.