added installation notes

updated the README because ref_points are now easier to add

added known limitations

Little secrets about the "show cap" map view

added further documentation

- Moved ref_points.php to something less toulouse-specific ;-)
by default : no ref points, but the ability to define its own list
or to use one of the files from ref_points folder.
- Fixed the UI if the ref_points list is empty.

added a README