Include information on legacy sideloading setting.

[jvintzel]

The doc should include that prior to Windows 10 2004 there was a setting needed to be enabled to install apps outside the Microsoft Store. Prior to Windows 10 2004 this setting was enabled by default on Windows 10 Home and Pro editions and needs to be enabled on Windows 10 Enterprise and LTS(B)C editions. Users can enable this setting in the settings app and enterprise can configure this via policy.

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Document Details

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• ID: 95b83f04-01b6-c494-1e2a-dcddecaa7dc8
• Version Independent ID: 758db7a1-fd48-56fc-1e82-0fbd7ad3f7dc
• Content: Supported platforms - MSIX
• Content Source: msix-src/supported-platforms.md
• Product: msix
• GitHub Login: @dianmsft
• Microsoft Alias: diahar

[RDMacLachlan]

Updated the Docs Article with the requested information. Updates are currently pending review...