add readme

README.md

+icebox-image-service
+====================
+
+This image service is simple. Put your image in the images directory and it will be available at `/<imagename>`.
+
+you can leave the fileextension empty and the typical image extensions will be guessed:
+
+`/premiumkola` will return `/premiumkola.png`, `/premiumkola.jpg` or `/premiumkola.jpeg`.