add hline breaks between overview sections

src/overview.md

@@ -20,6 +20,9 @@ pop-up "guided tour" explaining the key features. These tours will
 automatically start the first time a page is opened, or can be manually opened
 by clicking on the "Help" button on any of the main pages.
 
+
+----
+
 ## Compare
 
 The [Compare page](https://urbananalyst.city/compare) is the first and main
@@ -47,6 +50,8 @@ words brought up by clicking the "Explain Layer" button, "Low values indicate
 that good access to natural spaces is coupled with disadvantageous social
 conditions."
 
+----
+
 ## Map
 
 The [Map page](https://urbananalyst.city/map) shows interactive maps for each
@@ -63,6 +68,8 @@ values in brighter, yellow colours, while higher values are displayed in
 darker, blue or violet colours. The control panel includes an "Explain Layer"
 button which opens a text panel explaining details of the chosen variable.
 
+----
+
 ## Transform
 
 The [Transform page](https://urbananalyst.city/transform) enables the