address review feedbacks

Author: AllanZhengYP

smithy-typescript-codegen/src/main/java/software/amazon/smithy/typescript/codegen/integration/TypeScriptIntegration.java

@@ -162,7 +162,22 @@ default void writeAdditionalFiles(
 
     /**
      * Write additional export statement to client root index.ts.
-     * This is necessary when {@link TypeScriptIntegration#writeAdditionalFiles} is also implemented.
+     * The files generated by {@link TypeScriptIntegration#writeAdditionalFiles}
+     * can be exported with this method.
+     * 
+     * <pre>
+     * {@code
+     * public final class MyIntegration implements TypeScriptIntegration {
+     *     public writeAdditionalExports(
+     *             TypeScriptSettings settings,
+     *             Model model,
+     *             SymbolProvider symbolProvider,
+     *             TypeScriptWriter writer
+     *     ) {
+     *         writer.write("export * from $S;", "./foo.ts");
+     *     }
+     * }
+     * }</pre>
      *
      * @param settings Settings used to generate.
      * @param model Model to generate from.