docs: switches main button to be github (#373)

# Motivation

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# Content

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# Testing

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# Please check the following before marking your PR as ready for review

- [ ] I have added tests for my changes
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Author: jayhack

docs/mint.json

@@ -41,8 +41,8 @@
 		"thumbsRating": true
 	},
 	"topbarCtaButton": {
-		"name": "Codegen",
-		"url": "https://codegen.sh/new"
+		"name": "GitHub",
+		"url": "https://github.com/codegen-sh/codegen-sdk"
 	},
 	"tabs": [
 		{