update with @jstac comments

Author: mmcky

lectures/_toc.yml

@@ -12,12 +12,12 @@ parts:
   - file: business_cycle
   - file: inflation_history
   - file: inequality
-- caption: Essential Tools
+- caption: Foundations
   numbered: true
   chapters:
   - file: intro_supply_demand
-  - file: complex_and_trig
   - file: linear_equations
+  - file: complex_and_trig
 - caption: "Linear Dynamics: Finite Horizons"
   numbered: true
   chapters: