I have the following:

```
from django.contrib.auth.models import User

class ClientDetails(models.Model):
    created_by = models.ForeignKey(User)
    ...

```

How do I make `created_by` default to the currently logged in user?

*(I want to do this so I can hide it in the admin view mainly but also because when I save an instance I don't want to be filling it every time)*