[wasm-metadata] add example to README (#2057)

Author: yoshuawuyts

crates/wasm-metadata/src/lib.rs

@@ -1,4 +1,48 @@
 //! Read and manipulate WebAssembly metadata
+//!
+//! # Examples
+//!
+//! **Read metadata from a Wasm binary**
+//!
+//! ```no_run
+//! # #![allow(unused)]
+//! # fn main() -> Result<(), anyhow::Error> {
+//! use wasm_metadata::Payload;
+//! use std::fs;
+//!
+//! let wasm = fs::read("program.wasm")?;
+//! let metadata = Payload::from_binary(&wasm)?.metadata();
+//! # Ok(()) }
+//! ```
+//!
+//! **Add metadata to a Wasm binary**
+//!
+//! ```no_run
+//! # #![allow(unused)]
+//! # fn main() -> Result<(), anyhow::Error> {
+//! use wasm_metadata::*;
+//! use std::fs;
+//!
+//! let wasm = fs::read("program.wasm")?;
+//!
+//! let metadata = AddMetadata {
+//!     name: Some("program".to_owned()),
+//!     language: vec![("tunalang".to_owned(), "1.0.0".to_owned())],
+//!     processed_by: vec![("chashu-tools".to_owned(), "1.0.1".to_owned())],
+//!     sdk: vec![],
+//!     authors: Some(Authors::new("Chashu Cat")),
+//!     description: Some(Description::new("Chashu likes tuna")),
+//!     licenses: Some(Licenses::new("Apache-2.0 WITH LLVM-exception")?),
+//!     source: Some(Source::new("https://github.com/chashu/chashu-tools")?),
+//!     homepage: Some(Homepage::new("https://github.com/chashu/chashu-tools")?),
+//!     revision: Some(Revision::new("de978e17a80c1118f606fce919ba9b7d5a04a5ad")),
+//!     version: Some(Version::new("1.0.0")),
+//! };
+//!
+//! let wasm = metadata.to_wasm(&wasm)?;
+//! fs::write("program.wasm", &wasm)?;
+//! # Ok(()) }
+//! ```
 
 #![warn(missing_debug_implementations, missing_docs)]