[docs] Add database initialization instructions example-header

Add missing level 3 heade for DB example

Signed-off-by: jcjveraa <3942301+jcjveraa@users.noreply.github.com>

docs/user-guide/sync-waves.md

@@ -185,6 +185,7 @@ spec:
   backoffLimit: 2
 ```
 
+### Initialize or migrate a database before main application tries to start
 The following example runs a db migration command before the main sync operation (also in wave -1):
 ```yaml
 apiVersion: batch/v1