docs: Add missing serde requirement in example

src/lib.rs

@@ -12,6 +12,7 @@
 //! # Example, use the version numbers you need
 //! tide = "0.14.0"
 //! async-std = { version = "1.6.0", features = ["attributes"] }
+//! serde = { version = "1.0", features = ["derive"] }
 //!```
 //!
 //! # Examples