python: Document virNodeGetInfo bug
python: Document virNodeGetInfo bug

The memory size in virNodeGetInfo python API binding is reported in MiB
instead of KiB (like we have in C struct). However, there already might
be applications out there relying on this inconsistence so we can't
simply fix it. Document this sad fact as known bug.

libvirt/libvirt-python,cardoe/libvirt-python,libvirt/libvirt-python,libvirt/libvirt-python,cardoe/libvirt-python,cardoe/libvirt-python