updated readme with bugs

Added small section described quirks that can be seen with the test suite.
I think I will label this "Testing" or "Running test suite" as this sounds bad. :p We definitely need something like this, so I may just merge and then move around. 

Also I don't think there are (known) *bugs* in Windows for actual usage, it's just in the testing suite... maybe. So I'll first have another go on my Windows machine and see if your last PR fixes the test failure(s) :)