Testing Python Wrappers doc should mention PATH should be set for Windows install (Bug #1933)

In the Install Guide for OpenCV, in the section "Testing Python wrappers", it says "If you want to try Python samples without installing OpenCV, put cv.so and cv2.so (called cv.pyd and cv2.pyd on Windows) to opencv/samples/python directory, or rather add the directory containing cv.so/cv.pyd to PYTHONPATH".

However, this is not sufficient on Windows. On Windows, you must also set the PATH to point to the directory that includes the various OpenCV DLLs, otherwise it will give the message:

Traceback (most recent call last):
File "delaunay.py", line 9, in <module>
import cv2.cv as cv
ImportError: DLL load failed: The specified module could not be found.

The error is vague, and it sounds like there is something wrong with the cv2.pyd, when in fact it was simply unable to load the OpenCV dlls.

A sentence should be added that states that in addition to the PYTHONPATH, the PATH should be set to the directory that contains the OpenCV dlls.