Added lib build instructions

README.md

@@ -17,6 +17,8 @@ Max Planck Institute for Gravitational Physics
 1. Download and install the Qt framework as described above
    - Note for macOS when using MacPorts:
      - Run once: `sudo ln -s /opt/local/libexec/qt4/bin/qmake /opt/local/bin/qmake`
+1. Run the following command in the project's `lib` directory:
+   - `make`
 1. Run the following commands in the project's root directory:
    1. `qmake`
    1. `make`