update headings

Author: devalog

fern/products/api-def/openapi-pages/extensions/sdk-variables.mdx

@@ -9,7 +9,7 @@ The `x-fern-sdk-variables` extension allows you to define variables that are set
   SDK variables are supported in TypeScript (v2.6.3+), Python (v4.24.0+), and Java (v3.6.3+). Only string types are supported.
 </Note>
 
-## Usage
+## Configuration
 
 Define variables at the document level using `x-fern-sdk-variables`, then mark path parameters as variables using `x-fern-sdk-variable`:
 
@@ -41,7 +41,7 @@ paths:
             type: string
 ```
 
-### SDK usage
+## SDK usage
 
 Variables become required constructor parameters instead of being passed to individual method calls: