It’s a bit confusing to have two files called `README`, especially given
that `README.win32.md` only contains build instructions and none of the
other overview/contribution/bug reporting information that `README.md`
contains.

It feels like these would be better organised by having one top-level
`README.md`, and pointing to the Windows build instructions from there.

Signed-off-by: Philip Withnall <pwithnall@endlessos.org>