Shapes: mention inverted shapes in the introductory docs.

doc/shapes.dox

@@ -35,6 +35,12 @@ together using various operations.
 
 @section shapes-collection Available shapes
 
+%Magnum provides a set of simple shapes for collision detection, similarly to
+what is found in many other collision detection libraries. Additionally some
+shapes are provided in inverted form -- e.g. inverted box detects collisions on
+outside instead of inside, which might be useful for example to create bounds
+around platformer game level.
+
 @subsection shapes-1D One-dimensional shapes
 
 - @ref Shapes::Point "Shapes::Point*D" -- @copybrief Shapes::Point
@@ -51,6 +57,7 @@ line and point. Collision of two lines can be detected only in 2D.
 @subsection shapes-3D Three-dimensional shapes
 
 - @ref Shapes::Sphere "Shapes::Sphere*D" -- @copybrief Shapes::Sphere
+- @ref Shapes::InvertedSphere "Shapes::InvertedSphere*D" -- @copybrief Shapes::InvertedSphere
 - @ref Shapes::Cylinder "Shapes::Cylinder*D" -- @copybrief Shapes::Cylinder
 - @ref Shapes::Capsule "Shapes::Capsule*D" -- @copybrief Shapes::Capsule
 - @ref Shapes::AxisAlignedBox "Shapes::AxisAlignedBox*D" -- @copybrief Shapes::AxisAlignedBox