Doc fix: openAIChat.modelName is read\-only after construction

Author: MiriamScharnke

doc/functions/openAIChat.md

@@ -100,9 +100,10 @@ Optionally specify these properties at construction using name\-value arguments.
 
 Name of the OpenAI model to use for text generation.
 
-
 For information about currently supported models, see the OpenAI documentation at [https://platform.openai.com/docs/overview](https://platform.openai.com/docs/overview).
 
+After construction, this property is read\-only.
+
 ### `Temperature` — Temperature
 
 `1` (default) | numeric scalar between `0` and `2`