clarified need to assign specific drive letter

After a lot of try and error I stumbled over this. (I found the error logs on C:\)
Better solution would probably be a check during install, but that´s out of my scope.

docs/os/windows/windows-tools41.md

@@ -16,7 +16,8 @@ Qubes Windows Tools (QWT) are a set of programs and drivers that provide integra
    - Xen PV Disk Drivers: paravirtual storage drivers
    - Xen PV Network Drivers: paravirtual network drivers
    - Move user profiles: user profile directory (`C:\users`) is moved to VM's private disk backed by `private.img file` in `dom0` (useful mainly for HVM templates).
-	
+	> **Note**: If you choose to move profiles, drive letter Q: must be assigned to the secondary (private) disk.
+
 	> **Note**: Xen PV disk drivers are not installed by default. This is because they seem to cause problems (BSOD = Blue Screen Of Death). We're working with upstream devs to fix this. *However*, the BSOD seems to only occur after the first boot and everything works fine after that. **Enable the drivers at your own risk** of course, but we welcome reports of success/failure in any case (backup your VM first!). With disk PV drivers absent `qvm-block` will not work for the VM, but you can still use standard Qubes inter-VM file copying mechanisms. On the other hand, the Xen PV drivers allow USB device access even without QWT installation if `qvm-features stubdom-qrexec` is set as `1`
 
 Below is a breakdown of the feature availability depending on the windows version: