Update python_module.md doc (CMU-Perceptual-Computing-Lab#1145)

Author: esemeniuc

doc/modules/python_module.md

@@ -24,7 +24,7 @@ The Python API is rather simple: `op::Array<float>` and `cv::Mat` objects get ca
 ## Compatibility
 The OpenPose Python module is compatible with both Python 2 and Python 3 (default and recommended). In addition, it will also run in all OpenPose compatible operating systems. It uses [Pybind11](https://github.com/pybind/pybind11) for mapping between C++ and Python datatypes.
 
-To compile, enable `BUILD_PYTHON` in CMake-gui. In Windows, make sure you compile the whole solution (clicking the green play button does not compile the whole solution!). You can do that by right-click on the OpenPose project solution, and clicking in `Build Solution` (or individually building the PyOpenPose module).
+To compile, enable `BUILD_PYTHON` in CMake-gui, or run `cmake -DBUILD_PYTHON=ON ..` from your build directory. In Windows, make sure you compile the whole solution (clicking the green play button does not compile the whole solution!). You can do that by right-click on the OpenPose project solution, and clicking in `Build Solution` (or individually building the PyOpenPose module).
 
 Pybind selects the latest version of Python by default (Python 3). To use Python 2, change `PYTHON_EXECUTABLE` and `PYTHON_LIBRARY` flags in CMake-gui to your desired Python version.