Update isometry.rs
Fix formatting of documentation so that "A 3D isometry is composed of:" is on its own line.
@@ -21,6 +21,7 @@ use crate::geometry::{AbstractRotation, Point, Translation};
/// A 2D isometry is composed of:
/// - A translation part of type [`Translation2`](crate::Translation2)
/// - A rotation part which can either be a [`UnitComplex`](crate::UnitComplex) or a [`Rotation2`](crate::Rotation2).
+///
/// A 3D isometry is composed of:
/// - A translation part of type [`Translation3`](crate::Translation3)
/// - A rotation part which can either be a [`UnitQuaternion`](crate::UnitQuaternion) or a [`Rotation3`](crate::Rotation3).
