Update _config.yml

Author: DrDrij

lectures/_config.yml

@@ -55,6 +55,7 @@ sphinx:
       description: This website presents a set of lectures on quantitative economic modeling, designed and written by Thomas J. Sargent and John Stachurski.
       keywords: Python, QuantEcon, Quantitative Economics, Economics, Sloan, Alfred P. Sloan Foundation, Tom J. Sargent, John Stachurski
       google_analytics_id: UA-54984338-10
+      sticky_toc: true
     mathjax_config:
       TeX:
         Macros: