chore(cargo): add more crate metadata

Cargo.toml

@@ -1,10 +1,16 @@
 [package]
 name = "youtube-api"
 version = "0.1.0"
+license = "GPL-3.0"
 authors = ["Max Jöhnk <[email protected]>"]
+keywords = ["youtube", "api", "client", "youtube-dl"]
+repository = "https://github.com/maxjoehnk/youtube-rs"
+description = "Async Youtube API implementation in Rust"
 edition = "2018"
+categories = ["api-bindings", "multimedia::video"]
 
-# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+[badges]
+travis-ci = { repository = "maxjoehnk/youtube-rs", branch = "master" }
 
 [dependencies]
 failure = "0.1"