DOC: Added missing model_name to VetiverModel

[ganesh-k13]

Changes

• Added missing model_name to VetiverModel in README

As per

vetiver-python/vetiver/vetiver_model.py

Line 65 in a70a822

model_name: str,

model_name is not optional, hence example for failing.

Traceback (most recent call last):   
  File "/home/ganesh/os/mlops/vetiver-python/hostt.py", line 8, in <module>
    v = VetiverModel(model, save_ptype=True, ptype_data=X)                                                                                                                                                                            
TypeError: VetiverModel.__init__() missing 1 required positional argument: 'model_name'

[isabelizimm]

Ah, thank you for this 🙌 looks perfect!