Windows 64-bit python 11899

Clarify the Windows install doc to say 64 bit python does work.

If you want to try this for yourself (I tested this on a clean Windows 7 Virtualbox image) and can't be bothered to download everything copies of the binaries used are in `ome:team/simon/windows/python_64bit_omero/`

See https://trac.openmicroscopy.org.uk/ome/ticket/11899#comment:14 for more details.