Update README.md

Author: pixelogik

README.md

@@ -6,10 +6,14 @@ My learning purpose is done with this project so further improvements that are o
 
 # How to build
 
+```
 cargo build
+```
 
 # How to render
 
 The output image is being written in the text format PPM to the standard output stream. The geometry, light and raytracing parameters are in the code in various files.
 
+```
 cargo run > image.ppm
+```