Generate field description rather than docstring in FragmentsPlugin?

Hi, thanks for this great library.
I'm trying to generate a fragment with descriptions but it gives the code like:

```py
class UserFragment(BaseModel):
    username: str
    "A login ID"
```

Is there an option to generate a description rather than docstring?

```py
class UserFragment(BaseModel):
    username: str = Field(description="A login ID")
```
