This will install the library to /usr/lib and the headers to /usr/include/docpp.
If you use Arch Linux, you can install the library by specifying -DBUILD_ARCH=ON to the cmake build command. This requires makepkg. If you don't specify anything, a PKGBUILD will be generated in the build directory.
If you use Gentoo Linux, an ebuild will automatically be generated in the build directory.
If you use a package manager that uses DEB or RPM packages, you can enable the BUILD_DEB or BUILD_RPM options to generate a package, which will be placed in the build directory.