add linestring faceview example

Author: SimonDanisch

src/GeometryBasics.jl

@@ -178,6 +178,10 @@ x[1] isa Triangle == true
 x isa AbstractVector{<: Triangle} == true
 # This means we can use it as a mesh:
 Mesh(x) # should just work!
+Can also be used for Points:
+
+linestring = FaceView(points, LineFace[...])
+Polygon(linestring)
 ```
 """
 struct FaceView{