Follow-up from Windows build fixes

[redstrate]

From #23:

a couple other notes from stuff i ran into, but which aren't changed in this PR:
windows-build.ps1 needs QTDIR environment variable to be set, not mentioned in BUILDING.md

Qt 9 was the lowest version that worked (QT_MIN_VERSION is 8 and BUILDING.md mentions Qt 6)

needs a python version with lxml installed (the CI scripts already handle this but the build docs should probably mention it for manual builds)

the copying over of the sqlite dll would also need to be added to the CI scripts, I only added it to the powershell build script here