Add keyword hasher.

See rust-lang/rust#77996

Author: tkaitchuck

Cargo.toml

@@ -5,7 +5,7 @@ authors = ["The Rust Project Developers"]
 description = "speed, non-cryptographic hash used in rustc"
 license = "Apache-2.0/MIT"
 readme = "README.md"
-keywords = ["hash", "fxhash", "rustc"]
+keywords = ["hash", "hasher", "fxhash", "rustc"]
 repository = "https://github.com/rust-lang-nursery/rustc-hash"
 
 [features]