config(errors): add better description to SchemaError

leapp/actors/config.py

@@ -44,7 +44,11 @@
 
 
 class SchemaError(Exception):
-    """Raised when a schema fails validation."""
+    """
+    Raised when actors use conflicting schemas.
+    
+    For example, one schema wants `section.field` to be an integer and other schema wants `section.field` to be a string.
+    """
 
 
 class ValidationError(Exception):