Include strawberry-sqlalchemy docs

[Ckk3]

Feature Request Type

• Core functionality
• Alteration (enhancement/optimization) of existing feature(s)
• New behavior

Description

We should update the main documentation to reference and include usage details for the strawberry-sqlalchemy project. This will help users discover and understand how to use Strawberry with SQLAlchemy through our extension.

We can use this PR, which adds Django documentation, as a reference.