Fix duplicate Sponsors section in grok package readme

[Copilot]

The Sponsors section was appearing three times in the grok NuGet package readme.

The src/Grok/readme.md includes the #cli section from the main readme, which previously also included the sponsors footer. Since the Grok readme also has its own sponsors footer include, this caused duplication.

Added a closing <!-- #cli --> marker in the main readme.md before the sponsors section to properly end the #cli section. Now when the Grok readme includes the #cli section, it only gets the CLI content, and then includes the sponsors footer once via its own include directive.

Original prompt

The Sponsors section is cloned three times in the grok package readme. Fix that. See https://www.nuget.org/packages/grok (and contrast with https://www.nuget.org/packages/xAI).

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[kzu]

@copilot we should instead close the cli section before the sponsors section (with a matching <!-- #cli -->) and instead include the raw footer form the CLI readme.

[Copilot]

@copilot we should instead close the cli section before the sponsors section (with a matching <!-- #cli -->) and instead include the raw footer form the CLI readme.

Done in 2361a70. Added the closing <!-- #cli --> marker in the main readme before the sponsors section, and restored the direct footer include in the Grok readme.