Update _episodes/03-configuration.md

Co-authored-by: Manuel Schlund <32543114+schlunma@users.noreply.github.com>

Author: LisaBock

_episodes/03-configuration.md

@@ -20,7 +20,7 @@ keypoints:
 
 ---
 
-## The configuration file 
+## Configuring ESMValTool via YAML files
 
 ESMValTool provides a list of default configuration files, e.g. 
 the ``config-user.yml`` configuration file contains all the global level