Add instructions on how to disable BitLocker encryption on Windows

[aknierim]

We should add instructions on how to disable BitLocker to the dual boot guide.

BitLocker is a feature available on newer versions* of Windows and encrypts everything on the drive Windows is installed on. Problems arise, when one tries to install Linux alongside Windows and disables secure boot in the BIOS. This prompts BitLocker to encrypt the drive, thus making it impossible to boot without the BitLocker recovery key. Since most people aren't even aware of the feature, finding the recovery key can be bothersome, if not impossible.

BitLocker should thus be disabled before disabling secure boot in the BIOS. This can be done by selecting
Start > Settings > Privacy & security > Device encryption > BitLocker drive encryption
or searching for BitLocker in the settings.

*BitLocker is not available on Windows 10 Home edition, but on the Pro edition and all editions of Windows 11.

[maxnoe]

Here are instructions for disabling and then re-enabling them again afterwards:
https://itsfoss.com/dual-boot-ubuntu-windows-bitlocker/

I think it's important not to give the message "you have to disable disk encryption for this to work"