Document existence of the serde feature

Author: arcnmx

README.md

@@ -28,6 +28,7 @@ extern crate enumflags2;
 - [x] Has a similar API compared to the popular [bitflags](https://crates.io/crates/bitflags) crate.
 - [x] Does not expose the generated types explicity. The user interacts exclusively with `struct BitFlags<Enum>;`.
 - [x] The debug formatter prints the binary flag value as well as the flag enums: `BitFlags(0b1111, [A, B, C, D])`.
+- [x] Optional support for serialization with the [`serde`](https://serde.rs/) feature flag.
 
 ### Example
 

enumflags/src/lib.rs

@@ -40,6 +40,10 @@
 //!     assert!(!(a_b.intersects(Test::C | Test::D)));
 //! }
 //! ```
+//!
+//! ## Optional Feature Flags
+//!
+//! - [`serde`](https://serde.rs/) implements `Serialize` and `Deserialize` for `BitFlags<T>`.
 #![warn(missing_docs)]
 #![cfg_attr(not(test), no_std)]