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

Jud White

2018-03-25 c6ecf1e0420737eafeb99b27b1d716b46a6cbb7a

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classes= 20
train  = data/train_voc.txt
valid  = data/voc/2007_test.txt
#difficult = data/voc/difficult_2007_test.txt
names = data/voc.names
backup = backup/