Improve PowerShell command to use wildcards for input data

In `Note for Windows users` it is more practical to use the following PowerShell command:

```powershell
$files = Get-ChildItem *.gz | Select-Object -Expand FullName

ena-upload-cli --dev --action add --center 'XXX' --data $files --checklist XXX --secret XXX --xlsx XXX.xlsx
```