Add description to Cargo.toml

Cargo.toml

@@ -3,6 +3,9 @@ name = "unwinding"
 version = "0.1.0"
 authors = ["Gary Guo <gary@garyguo.net>"]
 edition = "2018"
+license = "MIT OR Apache-2.0"
+description = "Unwinding library in Rust and for Rust"
+repository = "https://github.com/nbdd0121/unwinding/"
 
 [workspace]
 members = ["cdylib", "example"]