Docs request: if `pk` will be unique

[jamesbraza]

Is your feature request related to a problem? Please describe.

This model:

from tortoise.models import Model

class Foo(Model):
    id = fields.CharField(max_length=32, pk=True)

And reading docs here: https://tortoise.github.io/models.html?h=primary+key#primary-keys

Don't indicate if pk will be unique or not.

Describe the solution you'd like

Can we document in the primary keys docs that pk means unique, or doesn't mean unique?

Describe alternatives you've considered

N/a

Additional context

None

[vlakius]

it's a primary key...they are unique by design..