update hebberr_combo link

Author: rcoreilly

content/1-simulations/index.md

@@ -48,7 +48,7 @@ Here's a full list of all the simulations and the textbook exercise questions as
 
 * [family_trees](https://compcogneuro.org/sims/ch4/family_trees): Learning in a deep (multi-hidden-layer) network, showing advantages of combination of self-organizing and error-driven learning (Questions **4.8 -- 4.9**).
 
-* `hebberr_combo`: Hebbian learning in combination with error-driven facilitates generalization (Questions **4.10 -- 4.12**).
+* [hebberr_combo](https://compcogneuro.org/sims/ch4/hebberr_combo): Hebbian learning in combination with error-driven facilitates generalization (Questions **4.10 -- 4.12**).
 
 Note: no sims for chapter 5