Add "Correct Usage" and "Incorrect Usage" headings

java/ql/src/Violations of Best Practice/Undesirable Calls/DoNotCallFinalize.md

@@ -8,6 +8,8 @@ Avoid calling `finalize()` in application code. Allow the JVM to determine a gar
 
 ## Example
 
+### Incorrect Usage
+
 ```java
 class LocalCache {
     private Collection<File> cacheFiles = ...;
@@ -21,6 +23,8 @@ void main() {
 }
 ```
 
+### Correct Usage
+
 ```java
 import java.lang.AutoCloseable;
 import java.lang.Override;