Add description to spirv-std-macros

Author: hrydgard

crates/spirv-std-macros/Cargo.toml

@@ -5,6 +5,7 @@ authors = ["Embark <opensource@embark-studios.com>"]
 edition = "2018"
 license = "MIT OR Apache-2.0"
 repository = "https://github.com/EmbarkStudios/rust-gpu"
+description = "Macros for spirv-std"
 
 [lib]
 proc-macro = true