docs[callbacks]: update to the FileCallbackHandler documentation (#20496)

**Description:** Update to the `FileCallbackHandler` documentation
**Issue:** #20493 
**Dependencies:** None

docs/docs/modules/callbacks/filecallbackhandler.ipynb

@@ -5,8 +5,11 @@
    "id": "63b87b91",
    "metadata": {},
    "source": [
-    "# Logging to file\n",
-    "This example shows how to print logs to file. It shows how to use the `FileCallbackHandler`, which does the same thing as [`StdOutCallbackHandler`](/docs/modules/callbacks/#get-started), but instead writes the output to file. It also uses the `loguru` library to log other outputs that are not captured by the handler."
+    "# File logging\n",
+    "\n",
+    "LangChain provides the `FileCallbackHandler` to write logs to a file. The `FileCallbackHandler` is similar to the [`StdOutCallbackHandler`](/docs/modules/callbacks/), but instead of printing logs to standard output it writes logs to a file.\n",
+    "\n",
+    "We see how to use the `FileCallbackHandler` in this example. Additionally we use the `StdOutCallbackHandler` to print logs to the standard output. It also uses the `loguru` library to log other outputs that are not captured by the handler."
    ]
   },
   {
@@ -45,8 +48,7 @@
     }
    ],
    "source": [
-    "from langchain.callbacks import FileCallbackHandler\n",
-    "from langchain.chains import LLMChain\n",
+    "from langchain_core.callbacks import FileCallbackHandler, StdOutCallbackHandler\n",
     "from langchain_core.prompts import PromptTemplate\n",
     "from langchain_openai import OpenAI\n",
     "from loguru import logger\n",
@@ -54,16 +56,18 @@
     "logfile = \"output.log\"\n",
     "\n",
     "logger.add(logfile, colorize=True, enqueue=True)\n",
-    "handler = FileCallbackHandler(logfile)\n",
+    "handler_1 = FileCallbackHandler(logfile)\n",
+    "handler_2 = StdOutCallbackHandler()\n",
     "\n",
-    "llm = OpenAI()\n",
     "prompt = PromptTemplate.from_template(\"1 + {number} = \")\n",
+    "model = OpenAI()\n",
     "\n",
     "# this chain will both print to stdout (because verbose=True) and write to 'output.log'\n",
     "# if verbose=False, the FileCallbackHandler will still write to 'output.log'\n",
-    "chain = LLMChain(llm=llm, prompt=prompt, callbacks=[handler], verbose=True)\n",
-    "answer = chain.run(number=2)\n",
-    "logger.info(answer)"
+    "chain = prompt | model\n",
+    "\n",
+    "response = chain.invoke({\"number\": 2}, {\"callbacks\": [handler_1, handler_2]})\n",
+    "logger.info(response)"
    ]
   },
   {
@@ -166,7 +170,7 @@
    "name": "python",
    "nbconvert_exporter": "python",
    "pygments_lexer": "ipython3",
-   "version": "3.11.6"
+   "version": "3.9.6"
   }
  },
  "nbformat": 4,