Updated Windows Build Instructions for python > 3.8

[f-o-n]

Added some extra details to the windows build instructions to get it work with python > 3.8. I was able to build it with mercuryapi-AHAB-1.35.2.72-1 and and latest mercuryapi-BILBO-1.37.3.29.

To make 1.37.2 work the changes from https://github.com/gotthardp/python-mercuryapi/pull/148 were also required. It also did not come with the pthreads source anymore which had to be copied over.