Cargo.toml: add toml file

Cargo.toml

+[package]
+name = "gbl"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+clap = { version = "3.1.17", features = ["derive"] }
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