update comment, json is no longer supported

src/node/config.ts

@@ -169,7 +169,7 @@ export async function resolveConfig(
   return config
 }
 
-export const supportedConfigExtensions = ['js', 'ts', 'mjs', 'mts']
+const supportedConfigExtensions = ['js', 'ts', 'mjs', 'mts']
 
 export function isAdditionalConfigFile(path: string) {
   const filename_to_check = path.split('/').pop() ?? ''

src/node/siteConfig.ts

@@ -194,7 +194,7 @@ export interface UserConfig<ThemeConfig = any>
 
   /**
    * Multi-layer configuration overloading.
-   * Auto-resolves to `docs/.../config.(ts|js|json)` when unspecified.
+   * Auto-resolves to `docs/.../config.{js,mjs,ts,mts}` when unspecified.
    *
    * Set to `{}` to opt-out.
    *