Mention how to get the current compiler version in version documentat…

…ion (#4170)

crates/typst/src/foundations/version.rs

@@ -18,6 +18,8 @@ use crate::foundations::{cast, func, repr, scope, ty, Repr};
 /// special case, the empty version (that has no components at all) is the same
 /// as `0`, `0.0`, `0.0.0`, and so on.
 ///
+/// The current version of the Typst compiler is available as `sys.version`.
+///
 /// You can convert a version to an array of explicitly given components using
 /// the [`array`] constructor.
 #[ty(scope, cast)]