doc/encoders: fix libfdk-aac "Examples" subsection

Signed-off-by: Timothy Gu <timothygu99@gmail.com>
Signed-off-by: Stefano Sabatini <stefasab@gmail.com>

doc/encoders.texi

@@ -748,7 +748,7 @@ about 80-96 kbps/channel
 Default value is 0.
 @end table
 
-@section Examples
+@subsection Examples
 
 @itemize
 @item