Update `gh repo create` documentation

[meiji163]

Code of Conduct

• I have read and agree to the GitHub Docs project's Code of Conduct

What article on docs.github.com is affected?

• Create a repo
• Adding an existing project to GitHub using the command line
• Creating GitHub CLI extensions

What changes are you suggesting?

Update the documentation for gh repo create to reflect the new usage, which is set to be merged in the next release of GitHub CLI
Ref: cli/cli#4578, cli/cli#4567

Additional information

No response

[welcome]

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