Add database engine doc to the menu (#6029)

docs/generator/buildyaml.sh

@@ -156,6 +156,7 @@ echo -ne "        - Running behind another web server:
 "
 #navpart 2 system
 navpart 2 database
+navpart 2 database/engine
 navpart 2 registry
 
 echo -ne "    - 'docs/Performance.md'