[FEATURE] Document errors

### Issue to be solved

As initially brought up in https://github.com/onflow/cadence/issues/3711, it could be helpful to have a section in http://cadence-lang.org for errors, and explain each error here. Examples of this have been done in [TS](https://typescript.tv/errors/#ts1006) and [Rust](https://doc.rust-lang.org/error_codes/E0015.html).