Updated image path.

Author: CnlPepper

README.md

@@ -20,7 +20,7 @@ The aims of the Raysect project are as follows:
 The general development philosophy is ease of use trumps performance, but performance is not to be ignored.
 
 
-![Dispersion of light passing through a prism](docs/source/demonstrations/prism_720x360.jpg)
+![Dispersion of light passing through a prism](docs/source/demonstrations/optics/prism_720x360.jpg)
 
 *Caption: a simulation of Newton's classic experiment, white light being dispersed by a glass prism.*