Add model parameter doc for OpenAI embeddings

docs/integrations/builtin/cluster-nodes/sub-nodes/n8n-nodes-langchain.embeddingsopenai.md

@@ -22,6 +22,7 @@ For usage examples and templates to help you get started, refer to n8n's [OpenAI
 
 ## Node options
 
+* **Model**: The model to use for generating embeddings.
 * **Base URL**: the URL to send the request to. Use this if you are using a self-hosted OpenAI-like model. 
 * **Batch Size**: maximum number of documents to send in each request.
 * **Strip New Lines**: whether to remove new line characters from input text. n8n enables this by default.