bevy_reflect: Add crate level functions feature docs (#15086)

Adds the missing section for the `functions` cargo feature of the
`bevy_reflect` crate.

crates/bevy_reflect/src/lib.rs

@@ -454,15 +454,11 @@
 //! but [`Reflect`] requires all types to have a `'static` lifetime.
 //! This makes it impossible to reflect any type with non-static borrowed data.
 //!
-//! ## Function Reflection
+//! ## Generic Function Reflection
 //!
-//! Another limitation is the inability to fully reflect functions and methods.
-//! Most languages offer some way of calling methods dynamically,
-//! but Rust makes this very difficult to do.
-//! For non-generic methods, this can be done by registering custom [type data] that
-//! contains function pointers.
-//! For generic methods, the same can be done but will typically require manual monomorphization
-//! (i.e. manually specifying the types the generic method can take).
+//! Another limitation is the inability to reflect over generic functions directly. It can be done, but will
+//! typically require manual monomorphization (i.e. manually specifying the types the generic method can
+//! take).
 //!
 //! ## Manual Registration
 //!
@@ -485,6 +481,17 @@
 //! These dependencies are used by the [Bevy] game engine and must define their reflection implementations
 //! within this crate due to Rust's [orphan rule].
 //!
+//! ## `functions`
+//!
+//! | Default | Dependencies |
+//! | :-----: | :-------------------------------: |
+//! | ❌ | [`bevy_reflect_derive/functions`] |
+//!
+//! This feature allows creating a [`DynamicFunction`] or [`DynamicFunctionMut`] from Rust functions. Dynamic
+//! functions can then be called with valid [`ArgList`]s.
+//!
+//! For more information, read the [`func`] module docs.
+//!
 //! ## `documentation`
 //!
 //! | Default | Dependencies |
@@ -540,6 +547,10 @@
 //! [`smallvec`]: https://docs.rs/smallvec/latest/smallvec/
 //! [orphan rule]: https://doc.rust-lang.org/book/ch10-02-traits.html#implementing-a-trait-on-a-type:~:text=But%20we%20can%E2%80%99t,implementation%20to%20use.
 //! [`bevy_reflect_derive/documentation`]: bevy_reflect_derive
+//! [`bevy_reflect_derive/functions`]: bevy_reflect_derive
+//! [`DynamicFunction`]: crate::func::DynamicFunction
+//! [`DynamicFunctionMut`]: crate::func::DynamicFunctionMut
+//! [`ArgList`]: crate::func::ArgList
 //! [derive `Reflect`]: derive@crate::Reflect
 
 extern crate alloc;