docs(context_chat): Mention that embedding model shouldn't be changed after installation

admin_manual/ai/app_context_chat.rst

@@ -119,6 +119,8 @@ Listed below are the major parts of the system that can be scaled independently
    | The embedding model performance can be scaled by using a hosted embedding service, locally or remotely hosted. It should be able to serve an OpenAI-compatible API.
    | The embedding service URL can be set using the environment variable ``CC_EM_BASE_URL`` during deployment in the "Deploy Options". Other options like the model name, api key, or username and password can be set using the environment variables ``CC_EM_MODEL_NAME``, ``CC_EM_API_KEY``, ``CC_EM_USERNAME``, and ``CC_EM_PASSWORD`` respectively.
 
+   | Note that you cannot change the embedding model after installing the app, so if you want to use a different embedding model or service you will need to do a full uninstall (removing all data of the ExApp) and reinstall the ``context_chat_backend`` ExApp with the new environment variables and an empty vectorDB. If the vectorDB is external, the connected database (can be `ccb`) should be dropped before installing the ExApp again.
+
 One part of the system that cannot be scaled yet is the parsing of the documents to extract text.
 This is currently done in a single instance of the ``context_chat_backend`` ExApp.
 It is a CPU-bound task so having a powerful CPU will help speed up the parsing process.