Add install instructions to cmake rules

[justsz]

This PR adds the cmake ability to install the package.

The following is now possible:

cmake -DCMAKE_INSTALL_PREFIX=${INSTALL_DIR} -DBUILD_SHARED_LIBS=Yes ..
cmake --build .
cmake --install .

Afterward, INSTALL_DIR will contain:

INSTALL_DIR
├── lib
│   ├── libfortran-yaml-c.so
│   ├── liblibyaml_interface.so
│   └── libyaml.so
└── modules
    ├── fortran_yaml_c_interface.mod
    ├── fortran_yaml_c.mod
    └── fortran_yaml_c_types.mod

[Nicholaswogan]

Thanks for this!