Update README.windows.md

added supporting information in cases when packages are failing to build in Windows
Send debug output to right place
fix #5154 (nested for loop syntax & break behavior)
Defines +,- for Triangular matrices

Fix #5927
Windows: download busybox-win32 during make win-extras

copy it to echo.exe and printf.exe during make dist
This allows test/spawn.jl to succeed on Windows, since echo and printf
are only included as shell scripts in msysgit (and an echo.bat in
contrib/windows), but libuv cannot spawn shell or bat scripts.
Add OPENBLAS_NO_AVX build option to disable AVX kernels

useful for compiling with OPENBLAS_DYNAMIC_ARCH = 1 using old binutils versions
Fix check for BUILD_LLVM_CLANG when LLVM_VER=svn.
sparse optimizations
Appears to fix #7488.
Some ARPACK inteface tweaks.
Merge pull request #7483 from tanmaykm/tanmaykm

sparse indexing performance improvement.
Don't trincate stride in geqp3
Fix a type ambiguity in umfpack definitions.
Merge branch 'master' of github.com:JuliaLang/julia
add test/goto.jl to runtests.jl

apparently missed from #5699
fix bug in readall(TTY), and modify a repl test to sometimes trigger this potential race condition
Simplify implementation of centralize_sumabs2

Also fix a bounds violation when computing the variance of a vector
with a single element
Add a string constructor to VersionNumber

I feel this is more natural than `convert(VersionNumber, mystring)`, but maybe there was a design reason behind this
Merge pull request #7492 from JuliaLang/sjk/centralize_sumabs2

Simplify implementation of centralize_sumabs2
Merge pull request #6516 from fruser/patch-1

Update README.windows.md
Use access/_waccess for isreadable