UI updates. (#6398)

### What problem does this PR solve?

Updated UI descriptions for delimiters and recommended chunk size

### Type of change

- [x] Documentation Update

docs/guides/chat/accelerate_question_answering.mdx

@@ -14,6 +14,12 @@ Please note that some of your settings may consume a significant amount of time.
 
 - In the **Prompt Engine** tab of your **Chat Configuration** dialogue, disabling **Multi-turn optimization** will reduce the time required to get an answer from the LLM.
 - In the **Prompt Engine** tab of your **Chat Configuration** dialogue, leaving the **Rerank model** field empty will significantly decrease retrieval time.
+- When using a rerank model, ensure you have a GPU for acceleration; otherwise, the reranking process will be *prohibitively* slow.
+
+:::tip NOTE 
+Please note that rerank models are essential in certain scenarios. There is always a trade-off between speed and performance; you must weigh the pros against cons for your specific case.
+:::
+
 - In the **Assistant Setting** tab of your **Chat Configuration** dialogue, disabling **Keyword analysis** will reduce the time to receive an answer from the LLM.
 - When chatting with your chat assistant, click the light bulb icon above the *current* dialogue and scroll down the popup window to view the time taken for each task:  
    ![enlighten](https://github.com/user-attachments/assets/fedfa2ee-21a7-451b-be66-20125619923c)  

docs/guides/models/llm_api_key_setup.md

@@ -30,7 +30,7 @@ You have two options for configuring your model API key:
    - Update `api_key` with yours.
    - Update `base_url` if you use a proxy to connect to the remote service.
 3. Reboot your system for your changes to take effect.
-4. Log into RAGFlow.
+4. Log into RAGFlow.  
    _After logging into RAGFlow, you will find your chosen model appears under **Added models** on the **Model providers** page._
 
 ### Configure model API key after logging into RAGFlow