Add no-std category to crates.io metadata

Cargo.toml

@@ -2,7 +2,7 @@
 name = "anyhow"
 version = "1.0.58" # remember to update html_root_url
 authors = ["David Tolnay <[email protected]>"]
-categories = ["rust-patterns"]
+categories = ["rust-patterns", "no-std"]
 description = "Flexible concrete Error type built on std::error::Error"
 documentation = "https://docs.rs/anyhow"
 edition = "2018"