message: features: Document the new optional_dependency field
diff: @@ -6,6 +6,7 @@ use serde::Serialize;
  pub struct Feature {
  pub(crate) name: String,
  pub(crate) subfeatures: Vec<String>,
  + /// [`None`] when this crate was built before optional dependencies were tracked
  pub(crate) optional_dependency: Option<bool>,
  }
  