README.md: add notes to How to compile on Windows

Jud White

2018-03-25 c6ecf1e0420737eafeb99b27b1d716b46a6cbb7a

 src/detection_layer.c

@@ -59,7 +59,7 @@
            for (i = 0; i < locations; ++i) {
                int offset = i*l.classes;
                softmax(l.output + index + offset, l.classes, 1,
                        l.output + index + offset);
                        l.output + index + offset, 1);
            }
        }
    }