chore: adjusting header size for section title

Author: alocay

docs/source/guides/index.mdx

@@ -275,7 +275,7 @@ npx @modelcontextprotocol/inspector
 
 1. Click **Connect** and **List Tools**. You should see the tools for the operations you provided.
 
-### Custom scalars configuration
+## Custom scalars configuration
 
 You can specify a custom scalars configuration JSON file to map a custom scalar to a [JSON schema type](https://json-schema.org/understanding-json-schema/reference/type). The JSON file is an object with custom scalar names as keys and JSON schema types as values:
 ```json