Installation notes tweak

[JohnPJenkins]

It would be a good idea to include the use of CMAKE_INSTALL_PREFIX and make install into the installation instructions, and the compiler/linker flags needed to compile against ROSS: -I/path/to/ROSS/install/include -L/path/to/ROSS/install/lib -lROSS. Additionally, the "Constructing the Model" and top level README pages should be updated accordingly. Not everyone will want to symlink their code into ROSS to build their models :).

[carns]

Rather than document the flags explicitly, it would be better to document the use of ross-config for this stuff. That way as long as ross-config is kept up to date then the documentation will be safe. ross-config can also tell you the CC that was used to compile ROSS (via ross-config --cc) as well if you want to make sure that everything matches up.

If we have a .pc file for package config thing we could document that too or in place of ross-config. It would provide similar functionality.