feat: add documentation for agent visualization using Graphviz

Author: MartinEBravo

docs/visualizations.md renamed to docs/visualization.md

@@ -7,7 +7,7 @@ Agent visualization allows you to generate a structured graphical representation
 The visualization functionality relies on the **Graphviz** package. To use it, ensure you have Graphviz installed and add it as a dependency in `pyproject.toml`. Alternatively, install it directly via pip:
 
 ```bash
-pip install graphviz
+pip install openai-agents[visualization]
 ```
 
 ## Generating a Graph
@@ -22,7 +22,7 @@ You can generate an agent visualization using the `draw_graph` function. This fu
 
 ```python
 from agents import Agent, function_tool
-from agents.visualizations import draw_graph
+from agents.extensions.visualization import draw_graph
 
 @function_tool
 def get_weather(city: str) -> str: