Clearly document what can be translated and what cannot

Original issue:

1- I think some details about what is supported and what is not instead of "many common scenarios" would be useful or at least a link to issues regarding this.

2- I think it would be great to configure EF core to opt in by default instead of manually opting in and having an opt out to support exceptions to this scenario. We have a big application and I am not a fan of opting in manually everywhere and then eventually removing that when it is mature enough that opting in is no longer necessary... It is a temporary patch that in painful to implement and then remove. We have expressions that are generated at run time with reusable bits and pieces here and there with tons of projection to get only what we need from the db... and the ToList opt-in is difficult in that case.