Add mock description to rustc-dependencies

Author: lnicola

crates/rustc-dependencies/Cargo.toml

@@ -1,6 +1,8 @@
 [package]
 name = "rustc-dependencies"
 version = "0.0.0"
+description = "TBD"
+
 rust-version.workspace = true
 edition.workspace = true
 license.workspace = true