more demos

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Readme.md

@@ -69,7 +69,7 @@ setobject!(vis, PointCloud(verts, colors))
 
 ![demo-points](https://user-images.githubusercontent.com/591886/36703986-3d18e232-1b2c-11e8-8c40-a73e55cc93b6.png)
 
-### Complex Geometries
+### Contours
 
 ```julia
 # Visualize a mesh from the level set of a function
@@ -83,6 +83,28 @@ setobject!(vis, mesh,
 
 ![demo-contour](https://user-images.githubusercontent.com/591886/36703981-37b62ba6-1b2c-11e8-90aa-4c38486732e7.png)
 
+### Polyhedra
+
+```
+# Visualize a polyhedron from Polyhedra.jl
+using Polyhedra
+using CDDLib
+# Construct a polyhedron in 4 dimensions
+ext1 = SimpleVRepresentation([0 1 2 3;0 2 1 3; 1 0 2 3; 1 2 0 3; 2 0 1 3; 2 1 0 3;
+                              0 1 3 2;0 3 1 2; 1 0 3 2; 1 3 0 2; 3 0 1 2; 3 1 0 2;
+                              0 3 2 1;0 2 3 1; 3 0 2 1; 3 2 0 1; 2 0 3 1; 2 3 0 1;
+                              3 1 2 0;3 2 1 0; 1 3 2 0; 1 2 3 0; 2 3 1 0; 2 1 3 0])
+poly1 = CDDPolyhedron{4,Rational{BigInt}}(ext1)
+
+# Project that polyhedron down to 3 dimensions for visualization
+poly2 = project(poly1, [1 1 1; -1 1 1; 0 -2 1; 0 0 -3])
+
+# Show the result
+setobject!(vis, poly2)
+```
+
+![polyhedron](https://user-images.githubusercontent.com/591886/37313984-fa3b20c2-2627-11e8-8238-71607a7f16e7.png)
+
 ### Mechanisms
 
 Using https://github.com/rdeits/MeshCatMechanisms.jl