fix: add import for gymnasium (#3899)

docs/use_cases/agent_simulations/gymnasium.ipynb

@@ -10,6 +10,16 @@
     "For many applications of LLM agents, the environment is real (internet, database, REPL, etc). However, we can also define agents to interact in simulated environments like text-based games. This is an example of how to create a simple agent-environment interaction loop with [Gymnasium](https://github.com/Farama-Foundation/Gymnasium) (formerly [OpenAI Gym](https://github.com/openai/gym))."
    ]
   },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "id": "f36427cf",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "!pip install gymnasium"
+   ]
+  },
   {
    "cell_type": "code",
    "execution_count": 50,