Added in bump mapping section

Added Interactive Horizon mapping paper from Microsoft Research. Interactive Horizon Mapping creates shadows on surfaces with bump mapping

computer_graphics/README.md

@@ -15,5 +15,8 @@
 ### Lighting
 * [Light Propagation Volumes in CryEngine 3](http://www.crytek.com/download/Light_Propagation_Volumes.pdf)
 
+### Bump mapping
+* [Interactive Horizon Mapping: Shadows for bump-mapped surfaces](http://research.microsoft.com/en-us/um/people/cohen/bs.pdf)
+
 ### Interior mapping
 * [Interior Mapping: A new technique for rendering realistic buildings](http://www.proun-game.com/Oogst3D/CODING/InteriorMapping/InteriorMapping.pdf)