Update constraint.rs

Author: madhav-madhusoodanan

crates/intrinsic-test/src/common/constraint.rs

@@ -1,9 +1,12 @@
 use serde::Deserialize;
 use std::ops::Range;
 
+/// Describes the values to test for a const generic parameter.
 #[derive(Debug, PartialEq, Clone, Deserialize)]
 pub enum Constraint {
+    /// Test a single value.
     Equal(i64),
+    /// Test a range of values, e.g. `0..16`.
     Range(Range<i64>),
 }