Add required Cargo.toml fields to pio-core (#77)

Author: 9names

pio-core/Cargo.toml

@@ -2,6 +2,9 @@
 name = "pio-core"
 version = "0.3.0"
 edition = "2021"
+license = "MIT"
+description = "Low-level internals for RP2040's PIO State Machines. You should use the pio crate instead."
+repository = "https://github.com/rp-rs/pio-rs"
 
 [dependencies]
 arrayvec = { version = "0.7", default-features = false }