Docs: specify the compatibility with SQLModel more explicitely

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### Summary

Hi there.
After browsing the documentation (and some issues/PR), I'm still not sure if `SQLModel` is properly supported at this time.
SQLModel objects have the particularity to be both Pydantic and SQLAlchemy objects, so in theory, it may work using `SQLAlchemyFactory`.

But after trying by myself with this code:

```python
import secrets

from polyfactory import Use
from polyfactory.factories.sqlalchemy_factory import SQLAlchemyFactory
from sqlmodel import Field, Relationship, SQLModel

def get_random_id() -> str:
return secrets.token_urlsafe(nbytes=16)

class Place(SQLModel, table=True):
id: str = Field(default_factory=get_random_id, primary_key=True)
name: str = Field(unique=True)
items: list["Item"] = Relationship(back_populates="place")

class Item(SQLModel, table=True):
id: str = Field(default_factory=get_random_id, primary_key=True)
name: str = Field(unique=True)
place_id: str = Field(default=None, foreign_key="place.id")
place: Place = Relationship(back_populates="items")

class PlaceFactory(SQLAlchemyFactory[Place]):
__set_relationships__ = True

class ItemFactory(SQLAlchemyFactory[Item]):
__set_relationships__ = True
place = Use(PlaceFactory.build)

def test_factories():
item = ItemFactory.build()
assert item.place_id == item.place.id # /!\ AssertionError, they are not the same
```

With this code, the relationship is not actually created with the factory. I guess it's because polyfactory does not detect the `Relationship()` field which is specific to SQLModel.

So:
- Is SQLModel supported?
- If not directly, is there a workaround?
- Is is possible to provide some documentation about it? I guess it would valuable for people coming from fastAPI (with SQLModel) to know if they should stick to factory-boy or not, or can use a more modern approach like polyfactory.

Thanks! Keep up the great work.

Start by reproducing the provided SQLModel example with SQLAlchemyFactory and inspect how relationship fields are handled. Document whether SQLModel is supported, any workaround identified by the investigation, and the expected relationship behavior when the documentation update is complete.

Written by the indexing model from the issue text.