chore: add licence to Cargo.toml

Author: ryangjchandler

Cargo.toml

@@ -2,6 +2,7 @@
 name = "php-parser-rs"
 description = "A handwritten recursive-descent parser for PHP written in Rust"
 keywords = ["php", "php-parser", "parser", "php-parser-rs", "php-ast"]
+license = "MIT"
 version = "0.0.0"
 edition = "2021"