Update custom_agent.ipynb (#2767)

Fixed an issue the agent is not taking the user's question as input.

Author: wangml999

docs/modules/agents/agents/custom_agent.ipynb

@@ -77,7 +77,7 @@
     "        Returns:\n",
     "            Action specifying what tool to use.\n",
     "        \"\"\"\n",
-    "        return AgentAction(tool=\"Search\", tool_input=\"foo\", log=\"\")\n",
+    "        return AgentAction(tool=\"Search\", tool_input=kwargs[\"input\"], log=\"\")\n",
     "\n",
     "    async def aplan(\n",
     "        self, intermediate_steps: List[Tuple[AgentAction, str]], **kwargs: Any\n",
@@ -92,7 +92,7 @@
     "        Returns:\n",
     "            Action specifying what tool to use.\n",
     "        \"\"\"\n",
-    "        return AgentAction(tool=\"Search\", tool_input=\"foo\", log=\"\")"
+    "        return AgentAction(tool=\"Search\", tool_input=kwargs[\"input\"], log=\"\")"
    ]
   },
   {