add code markup

Author: PhilippSalvisberg

docs/4-language-usage/2-variables-and-types/4-boolean-data-types/g-2410.md

@@ -26,6 +26,7 @@ END;
 
 ## Example (better)
 
+```
 DECLARE
    co_newFile CONSTANT PLS_INTEGER := 1000;
    co_oldFile CONSTANT PLS_INTEGER := 500;
@@ -38,6 +39,7 @@ BEGIN
    END IF;
 END;
 /
+```
 
 ## Example (good)