update INSTALL file

git-svn-id: https://hedgehog.fhcrc.org/bioconductor/trunk/madman/Rpacks/flowWorkspace@84845 bc3139a8-67e5-0310-9ffc-ced21a209358
Merge commit '0798f568ee58f85cbe0cf9609c4c45bb1ef4413c' into trunk
mark it as win32 only
close #126