add instructions to install preview for macOS

[TravisEz13]

add instructions to install preview for macOS
addresses #2573

Version(s) of document impacted

• Impacts 6.1 document
• Impacts 6.0 document
• Impacts 5.1 document
• Impacts 5.0 document
• Impacts 4.0 document
• Impacts 3.0 document

Reason(s) for not updating all version of documents

• The documented feature was introduced in version (list version here) of PowerShell
• This issue only shows up in version (list version(s) here) of the document
• This PR partially fixes the issue, and issue # tracks the remaining work

[zjalexander]

✅ Validation status: passed

File	Status	Preview URL	Details
reference/docs-conceptual/setup/Installing-PowerShell-Core-on-macOS.md	✅Succeeded

For more details, please refer to the build report.

Note: If you changed an existing file name or deleted a file, broken links in other files to the deleted or renamed file are listed only in the full build report.

[zjalexander]

✅ Validation status: passed

File	Status	Preview URL	Details
reference/docs-conceptual/setup/Installing-PowerShell-Core-on-macOS.md	✅Succeeded

For more details, please refer to the build report.

Note: If you changed an existing file name or deleted a file, broken links in other files to the deleted or renamed file are listed only in the full build report.