Update `fx.pass.graph_drawer` usage doc to draw fx graph (#95534)
Previous usage gave this error:
```
f.write(g.get_dot_graph().create_svg())
TypeError: write() argument must be str, not bytes
```
pydot has function to save to different types, e.g. `save_svg()`. I updated the usage doc working code.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/95534
Approved by: https://github.com/ezyang
