document representation of Option<unsafe fn()>

Author: BennoLossin

library/core/src/option.rs

@@ -130,12 +130,13 @@
 //! | [`Box<U>`] (specifically, only `Box<U, Global>`)                    | when `U: Sized`                                                      |
 //! | `&U`                                                                | when `U: Sized`                                                      |
 //! | `&mut U`                                                            | when `U: Sized`                                                      |
-//! | `fn`, `extern "C" fn`[^extern_fn]                                   | always                                                               |
+//! | `fn`, `extern "C" fn`[^extern_fn][^unsafe_fn]                       | always                                                               |
 //! | [`num::NonZero*`]                                                   | always                                                               |
 //! | [`ptr::NonNull<U>`]                                                 | when `U: Sized`                                                      |
 //! | `#[repr(transparent)]` struct around one of the types in this list. | when it holds for the inner type                                     |
 //!
 //! [^extern_fn]: this remains true for any argument/return types and any other ABI: `extern "abi" fn` (_e.g._, `extern "system" fn`)
+//! [^unsafe_fn]: this also remains true for the `unsafe` variants `unsafe fn` or `unsafe extern "abi" fn`
 //!
 //! Under some conditions the above types `T` are also null pointer optimized when wrapped in a [`Result`][result_repr].
 //!