Add discussion/assignment based on Z2pack to Topological insulators

[jaysau]

Think of ways to add discussion of the package below to searching the table for periodic materials in three dimensional topological insulators:

http://z2pack.ethz.ch/doc/1.1.9/index.html

This package provides a way to visualize topology of realistic materials/tightbinding model through motion of wannier functions which is nicely related to charge pumping.