Update WSL shutdown instructions for clarity by specifying PowerShell should be run as administrator before executing the shutdown command.

[Civon]

This PR addresses the issue where the first attempt to run wsl --shutdown using an unprivileged PowerShell fails.

Steps to Reproduce

1. Fill the VHD to its capacity and follow the instructions to fix the read-only fallback error.
2. In the Read-only fallback error section, use an unprivileged PowerShell to run wsl.exe --shutdown.
3. Observe the error as shown in the image below:
   

Solution

Run the command in a privileged PowerShell session.

[learn-build-service-prod]

Learn Build status updates of commit d08a15a:

✅ Validation status: passed

File	Status	Preview URL	Details
WSL/disk-space.md	✅Succeeded	View

For more details, please refer to the build report.

For any questions, please:

• Try searching the learn.microsoft.com contributor guides
• Post your question in the Learn support channel

[Civon]

FYR: I may also need to close Docker Desktop(on Windows) to not getting error Wsl/Service/CreateInstance/MountVhd/HCS/ERROR_SHARING_VIOLATION while running next command wsl.exe sudo e2fsck -f /dev/sdc