Auto merge of #6608 - rail-rain:note_on_as_conversions, r=phansch
Add a note to `as_conversions`
I have seen a couple of examples where there are some misunderstandings of `as_conversions` ([1](https://github.com/rust-lang/rust-clippy/issues/5890#issuecomment-
671852546), [2](https://github.com/rust-lang/rust-clippy/issues/6116#issuecomment-
704251710) and [3](https://github.com/rust-lang/rust-clippy/issues/6428)). This PR adds the note that explains its purpose and relationship with other `as` related casts. Open question: should I list every related lints for discoverbility, or just suggest how to find these? I chose the former because there's no way to list only and all `as` related lints (e.g. on All the Clippt Lints, 'cast' includes some noises, but `cast_` excludes some) even though I cannot guarantee the list will be updated to include future changes.
---
changelog: Add a note to the document of `as_conversions`