RELEASES.md: Add 1.58 release note for File::options stabilization

Author: joshtriplett

RELEASES.md

@@ -42,6 +42,7 @@ Stabilized APIs
 - [`{integer}::saturating_div`]
 - [`Option::unwrap_unchecked`]
 - [`NonZero{unsigned}::is_power_of_two`]
+- [`File::options`]
 
 These APIs are now usable in const contexts:
 
@@ -137,6 +138,7 @@ and related tools.
 [`{integer}::saturating_div`]: https://doc.rust-lang.org/stable/std/primitive.i8.html#method.saturating_div
 [`Option::unwrap_unchecked`]: https://doc.rust-lang.org/stable/std/option/enum.Option.html#method.unwrap_unchecked
 [`NonZero{unsigned}::is_power_of_two`]: https://doc.rust-lang.org/stable/std/num/struct.NonZeroU8.html#method.is_power_of_two
+[`File::options`]: https://doc.rust-lang.org/stable/std/fs/struct.File.html#method.options
 [`unix::process::ExitStatusExt::core_dumped`]: https://doc.rust-lang.org/stable/std/os/unix/process/trait.ExitStatusExt.html#tymethod.core_dumped
 [`unix::process::ExitStatusExt::stopped_signal`]: https://doc.rust-lang.org/stable/std/os/unix/process/trait.ExitStatusExt.html#tymethod.stopped_signal
 [`unix::process::ExitStatusExt::continued`]: https://doc.rust-lang.org/stable/std/os/unix/process/trait.ExitStatusExt.html#tymethod.continued