update kotlin option description to clarify the support (#20211)

Author: wing328

docs/generators/kotlin.md

@@ -27,7 +27,7 @@ These options may be applied as additional-properties (cli) or configOptions (pl
 |enumPropertyNaming|Naming convention for enum properties: 'camelCase', 'PascalCase', 'snake_case', 'UPPERCASE', and 'original'| |original|
 |explicitApi|Generates code with explicit access modifiers to comply with Kotlin Explicit API Mode.| |false|
 |failOnUnknownProperties|Fail Jackson de-serialization on unknown properties| |false|
-|generateOneOfAnyOfWrappers|Generate oneOf, anyOf schemas as wrappers.| |false|
+|generateOneOfAnyOfWrappers|Generate oneOf, anyOf schemas as wrappers. Only `jvm-retrofit2`(library), `gson`(serializationLibrary) support this option.| |false|
 |generateRoomModels|Generate Android Room database models in addition to API models (JVM Volley library only)| |false|
 |groupId|Generated artifact package's organization (i.e. maven groupId).| |org.openapitools|
 |idea|Add IntellJ Idea plugin and mark Kotlin main and test folders as source folders.| |false|

modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/KotlinClientCodegen.java

@@ -279,7 +279,7 @@ public KotlinClientCodegen() {
 
         cliOptions.add(new CliOption(MAP_FILE_BINARY_TO_BYTE_ARRAY, "Map File and Binary to ByteArray (default: false)").defaultValue(Boolean.FALSE.toString()));
 
-        cliOptions.add(CliOption.newBoolean(GENERATE_ONEOF_ANYOF_WRAPPERS, "Generate oneOf, anyOf schemas as wrappers."));
+        cliOptions.add(CliOption.newBoolean(GENERATE_ONEOF_ANYOF_WRAPPERS, "Generate oneOf, anyOf schemas as wrappers. Only `jvm-retrofit2`(library), `gson`(serializationLibrary) support this option."));
 
         CliOption serializationLibraryOpt = new CliOption(CodegenConstants.SERIALIZATION_LIBRARY, SERIALIZATION_LIBRARY_DESC);
         cliOptions.add(serializationLibraryOpt.defaultValue(serializationLibrary.name()));