Add section about building an auto-regressive model.
Add section about building an auto-regressive model.

jonathanrocher/pandas_tutorial,wateryhcho/pandas_tutorial,wateryhcho/pandas_tutorial,Sandor-PRA/pandas_tutorial,ajaykliyara/pandas_tutorial,ajaykliyara/pandas_tutorial,Sandor-PRA/pandas_tutorial,ajaykliyara/pandas_tutorial,wateryhcho/pandas_tutorial,linan7788626/pandas_tutorial,linan7788626/pandas_tutorial,jonathanrocher/pandas_tutorial,linan7788626/pandas_tutorial,jonathanrocher/pandas_tutorial,Sandor-PRA/pandas_tutorial