Update README.mingw32
Update README.mingw32

add option --prefix=/c/MinGW in order to install everything in the good directory
ld3300/ola,ld3300/ola,nightrune/ola,ld3300/ola,nightrune/ola,nightrune/ola,nightrune/ola,ld3300/ola,nightrune/ola,ld3300/ola,ld3300/ola,nightrune/ola,ld3300/ola,nightrune/ola