Update discovery PDF include code overview

Author: Philip Rees

book/discover.md

@@ -64,6 +64,10 @@ pages/tidal tools/analyze_database.md
 
 # Source code analysis
 
+```{.include}
+pages/user guides/code_analysis_overview.md
+```
+
 ```{.include}
 pages/tidal tools/sourcecode.md
 ```