chore: Improve crate keywords

Author: jhg

Cargo.toml

@@ -4,7 +4,7 @@ version = "0.4.0"
 description = "Generic functions to work with opaque pointers when use FFI to expose Rust structs"
 authors = ["Jesus Hernandez <jesushdez@protonmail.com>"]
 license = "Unlicense"
-keywords = ["pointer", "opaque", "pointers", "cbindgen"]
+keywords = ["pointer", "opaque", "pointers", "cbindgen", "ffi"]
 categories = ["development-tools::ffi", "no-std"]
 edition = "2018"
 readme = "README.md"