fix typo in documentation from relationship attribute and all manipulation of back populate

[AdamMusa]

I notice a few typo in documentation,so i decided to fix it .
I detected these errors because we did not take into consideration the key concept of sqlmodel concerning the back populate
Here is the key concept

That tells SQLModel that if something changes in this model, it should change that attribute in the other model, and it will work even before committing with the session (that would force a refresh of the data).

Here is the comparison considering the key concept of sqlmodel .
Here is some images after considering the key concept

![after_back_relationship_01](https://user-images.githubusercontent

.com/37194177/230231651-6a8c8f2d-5fee-476a-b7d6-225d8eacc153.png)

Here is some images before considering the key concept

[github-actions]

📝 Docs preview for commit 3f5683c at: https://642e022017a6b01f2da4bb7f--sqlmodel.netlify.app

[github-actions]

📝 Docs preview for commit 37bf39f at: https://642e09644dc21223dcf1b60a--sqlmodel.netlify.app

[github-actions]

📝 Docs preview for commit 7f356e1 at: https://52913fa7.sqlmodel.pages.dev

[tiangolo]

Thanks for the interest! That section refers to the updates in the Python objects. The database will be updated, but the objects are the ones that might not have all the updated data always... you can see the tests failing.

Given that, I'll pass on this one, but thanks for the effort. ☕