add readme file

poc/safeimage/readme.txt

+This POC shows that it is possible to display big images with Javascript.
+
+To see it, use your web browser and go to url [current_folder]/index.html
+
+Images are first splitted into many small images with ZoomifyImage
+(http://sourceforge.net/projects/zoomifyimage/) like this :
+
+python [path_to_zoomify]/ZoomifyFileProcessor.py image/original_image.jpg
+
+ZoomifyImage create a folder (with name of the image) coming with a file
+ImageProperties.xml (define size of image, number of tiles, etc), and several
+folders containing all splitted parts.
+
+Then only OpenLayers is used with Zoomify functions that comes directly with it.