chore(cargo): add documetation meta

Author: fundon

Cargo.toml

@@ -4,6 +4,7 @@ version = "0.7.0"
 authors = ["Fangdun Tsai <cfddream@gmail.com>"]
 description = "path-tree is a lightweight high performance HTTP request router for Rust"
 homepage = "https://github.com/viz-rs/path-tree"
+documentation = "https://docs.rs/path-tree"
 keywords = ["radix", "tree", "path", "router"]
 categories = ["asynchronous", "web-programming", "web-programming::http-server"]
 license = "MIT OR Apache-2.0"