SimpleMapServer small documentation

This documentation complete the README.TXT which is in the top folder.

There are details on:

1. the GIS data directory structure here.
2. the Google Earth superOverlays here.
3. the 'virtual' layers setting here.
4. the 'external' map producer module here.

And there are several layer configuration files in this folder.

gilles <dot> lavaux <at> serco <dot> com