docs: add helpful comments to sparkllm.py (langchain-ai#17774)

Adding helpful comments to sparkllm.py, help users to use ChatSparkLLM
more effectively

libs/community/langchain_community/chat_models/sparkllm.py

@@ -104,6 +104,18 @@ class ChatSparkLLM(BaseChatModel):
             spark_api_key="<api_key>",
             spark_api_secret="<api_secret>"
         )
+
+    Extra infos:
+        1. Get app_id, api_key, api_secret from the iFlyTek Open Platform Console:
+            https://console.xfyun.cn/services/bm35
+        2. By default, iFlyTek Spark LLM V3.0 is invoked.
+            If you need to invoke other versions, please configure the corresponding
+            parameters(spark_api_url and spark_llm_domain) according to the document:
+            https://www.xfyun.cn/doc/spark/Web.html
+        3. It is necessary to ensure that the app_id used has a license for
+            the corresponding model version.
+        4. If you encounter problems during use, try getting help at:
+            https://console.xfyun.cn/workorder/commit
     """
 
     @classmethod