Add note about git maintenance commands

[alexvy86]

Description

Adds notes about git maintenance run and git maintenance start to the repo README.

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[Copilot]

Pull Request Overview

This PR adds a new section in the README to provide guidance on using git maintenance commands.

• New "Repo maintenance" section added with descriptions for running "git maintenance run" and "git maintenance start".
• Removed environment-specific bullet points, replacing them with a cautionary note regarding potential system implications.

Comments suppressed due to low confidence (1)

README.md:212

• Consider clarifying what 'other implications' might be or including a reference to additional documentation for system-specific considerations related to 'git maintenance start'.

which could have other implications for your system, so proceed with caution.

[github-actions]

🔗 No broken links found! ✅

Your attention to detail is admirable.

linkcheck output

> fluid-framework-docs-site@0.0.0 ci:check-links /home/runner/work/FluidFramework/FluidFramework/docs
> start-server-and-test "npm run serve -- --no-open" 3000 check-links

1: starting server using command "npm run serve -- --no-open"
and when url "[ 'http://127.0.0.1:3000' ]" is responding with HTTP status code 200
running tests using command "npm run check-links"


> fluid-framework-docs-site@0.0.0 serve
> docusaurus serve --no-open

[SUCCESS] Serving "build" directory at: http://localhost:3000/

> fluid-framework-docs-site@0.0.0 check-links
> linkcheck http://localhost:3000 --skip-file skipped-urls.txt

Crawling...

Stats:
  222981 links
    1707 destination URLs
    1939 URLs ignored
       0 warnings
       0 errors