Update Reference on Decomposition Notebook

[renanxcortes]

Since our paper "Comparative Spatial Segregation Analytics" was accepted on Spatial Demography ( 👍 👍 👍 ) we can update the cell that says:

Let's decompose these difference according to Rey, S. et al "Comparative Spatial Segregation Analytics". Forthcoming. You can check the options available in this decomposition below:

In this notebook: https://github.com/pysal/segregation/blob/master/notebooks/decomposition_wrapper_example.ipynb

[knaaptime]

smart. when i'm finished with #161 we'll want to take another pass at the notebooks to update to the new api and show some new examples, so lets make sure to add the ref during that pass

[sjsrey]

Need to change the link to https://github.com/pysal/segregation/blob/master/notebooks/07_decomposition_example.ipynb