Add documentation

Signed-off-by: Gabor Mezei <gabor.mezei@arm.com>
diff --git a/scripts/config.py b/scripts/config.py
index 97d7555..3ee21d1 100755
--- a/scripts/config.py
+++ b/scripts/config.py
@@ -155,7 +155,11 @@
                 setting.active = enable
 
 def is_full_section(section):
-    """Is this section affected by "config.py full" and friends?"""
+    """Is this section affected by "config.py full" and friends?
+
+    In a config file where the sections are not used the whole config file
+    is an empty section (with value None) and the whole file is affected.
+    """
     return section is None or section.endswith('support') or section.endswith('modules')
 
 def realfull_adapter(_name, active, section):