Add description to backend crate

Author: alexcrichton

crates/backend/Cargo.toml

@@ -2,6 +2,13 @@
 name = "wasm-bindgen-backend"
 version = "0.2.0"
 authors = ["Nick Fitzgerald <[email protected]>"]
+license = "MIT/Apache-2.0"
+repository = "https://github.com/alexcrichton/wasm-bindgen"
+homepage = "https://github.com/alexcrichton/wasm-bindgen"
+documentation = "https://docs.rs/wasm-bindgen-backend"
+description = """
+Backend code generation of the wasm-bindgen tool
+"""
 
 [dependencies]
 quote = '0.5'