Add comment for how to set the CUDA path when cuda tools are installed b...

...y package manager.

This is a trivial modification to the Makefile.config.example file for installing on Ubuntu 14.04. 

Mainly I'm trying to see if I can figure out how github, git and "pull requests" work. This seemed like an innocuous change to submit. I expect you'll let me know if I'm doing something wrong.

BTW, to get it building on Ubuntu 14.04, I also had to modify the Makefile to specify g++-4.6 compiler instead of g++. But since I don't expect we want to hard-wire a particular compiler version in the Makefile, I left that change out.