Update overview.md

[lukemurraynz]

This pull request makes several improvements to the articles/governance/service-groups/overview.md documentation, focusing on grammar corrections, clarity enhancements, and consistency in terminology. These changes aim to make the content more readable and professional.

Grammar and Clarity Improvements:

• Fixed grammatical issues and improved sentence structure for better readability in the "Multiple Hierarchies" section.
• Enhanced the description of the "Flexible Membership" section to clarify the Service Groups model and improve sentence flow.
• Adjusted phrasing in the "Azure Resource Manager Groupings" section to improve clarity about containers and their purpose.

Consistency and Terminology:

• Corrected terminology in the "Service Group Contributor" section to ensure consistency and fix minor typos.

[prmerger-automator]

@lukemurraynz : Thanks for your contribution! The author(s) and reviewer(s) have been notified to review your proposed change. @rthorn17

[learn-build-service-prod]

Learn Build status updates of commit 1990258:

✅ Validation status: passed

File	Status	Preview URL	Details
articles/governance/service-groups/overview.md	✅Succeeded

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

[Court72]

@kenieva

Can you review the proposed changes?

Important: When the changes are ready for publication, adding a #sign-off comment is the best way to signal that the PR is ready for the review team to merge.

#label:"aq-pr-triaged"
@MicrosoftDocs/public-repo-pr-review-team