Add information about window layout saving

[Rosefield]

From

• Persist window layout cont. save multiple windows microsoft/terminal#11083 and
• Persist window layout on window close microsoft/terminal#10972

[opbld32]

Docs Build status updates of commit 79c83ed:

✅ Validation status: passed

File	Status	Preview URL	Details
TerminalDocs/customize-settings/startup.md	✅Succeeded	View

For more details, please refer to the build report.

Note: Broken links written as relative paths are included in the above build report. For broken links written as absolute paths or external URLs, see the broken link report.

For any questions, please:

• Try searching the docs.microsoft.com contributor guides
• Post your question in the Docs support channel

[opbld32]

Docs Build status updates of commit 10f3917:

✅ Validation status: passed

File	Status	Preview URL	Details
TerminalDocs/customize-settings/startup.md	✅Succeeded	View

For more details, please refer to the build report.

Note: Broken links written as relative paths are included in the above build report. For broken links written as absolute paths or external URLs, see the broken link report.

For any questions, please:

• Try searching the docs.microsoft.com contributor guides
• Post your question in the Docs support channel