Document that Is.InRange requires from <= to

docs/articles/nunit/writing-tests/constraints/RangeConstraint.md

@@ -28,7 +28,17 @@ Is.InRange(IComparable from, IComparable to)
 ## Notes
 
 1. The range is **inclusive** on both ends: `Is.InRange(1, 10)` passes for values 1, 10, and everything in between.
-2. For exclusive bounds, combine `Is.GreaterThan` and `Is.LessThan` with `And`:
+2. `from` must be less than or equal to `to`, otherwise the constraint throws an `ArgumentException`. Negative bounds
+   are fine, but the range must be written in increasing order: use `Is.InRange(-10, 0)`, not `Is.InRange(0, -10)`.
+   If the bounds are computed and could end up in either order, sort them first:
+
+   ```csharp
+   int lower = Math.Min(a, b);
+   int upper = Math.Max(a, b);
+   Assert.That(actual, Is.InRange(lower, upper));
+   ```
+
+3. For exclusive bounds, combine `Is.GreaterThan` and `Is.LessThan` with `And`:
 
    ```csharp
    Assert.That(5, Is.GreaterThan(1).And.LessThan(10));  // Exclusive bounds