chore(patch-hub-proc-macros): add package::{description,license} fields to crate

To publish a crate on crates.io it is good to have, at least, some
metadata in `Cargo.toml`. The `patch-hub-proc-macros` lacked
`description` and `license`, so add those to prepare the crate to be
published.

Signed-off-by: David Tadokoro <davidbtadokoro@usp.br>

Author: davidbtadokoro

patch_hub_proc_macros/Cargo.toml

@@ -2,6 +2,8 @@
 name = "patch-hub-proc-macros"
 version = "0.1.0"
 edition = "2021"
+description = "Crate for patch-hub procedural macros"
+license = "GPL-2.0"
 
 [dependencies]
 derive-getters = { version = "0.5.0", features = ["auto_copy_getters"] }