Update keywords in crates.io metadata

Author: dtolnay

Cargo.toml

@@ -6,6 +6,7 @@ categories = ["rust-patterns", "no-std"]
 description = "Flexible concrete Error type built on std::error::Error"
 documentation = "https://docs.rs/anyhow"
 edition = "2018"
+keywords = ["error", "error-handling"]
 license = "MIT OR Apache-2.0"
 readme = "README.md"
 repository = "https://github.com/dtolnay/anyhow"