cmake not installed as a dependency

[jennirinker]

Copy of NREL/ROSCO#42.

To compile ROSCO, users need to have cmake installed, which is not covered in the installation instructions.

EDIT: I tried the method below and it doesn't work. So for now, I will justs pip install cmake in any new environments before compiling.

If you assume that compiling ROSCO is a necessary function of the toolbox, then I think all you need to do is add cmake to the list of required packages in setup.py:

# These packages are required for all of the code to be executed. 
# - Maybe you can get away with older versions...
REQUIRED = [
    'cmake',
    'matplotlib',
    'numpy',
    'pytest',
    'scipy',
    'pyYAML',
]