list_base_model bug fix

[Occupying-Mars]

Added a default Basemodel for whenever tool use is being used in agent inside list_base_models. before it was set to none but it can't be set to none so i created a default one that passes the information as is also added a warning raise to let the user know to add his own base model. also updated main.md docs bug fixed: https://github.com/kyegomez/swarms/issues/605

---

📚 Documentation preview 📚: https://swarms--648.org.readthedocs.build/en/648/