Seaborn requires all the data we want to plot in one DataFrame
We use pd.concat to concatenate molten_plot_company and molten_plot_industry
molten_plot_industry does not have the company DataFrame because it contains the
average of the ratios per industry overall
pd.concat requires both DataFrames should to have the same columns, so we add the
column company to molten_plot_industry
molten_plot_industry["company"] = "Industry Average"
molten_plot = pd.concat([molten_plot_company, molten_plot_industry])