SONAR-10246 Fix documentation about default group in sso authentication

sonar-application/src/main/assembly/conf/sonar.properties

@@ -164,8 +164,8 @@
 
 # Name of the header to get the list of user groups, separated by comma (optional).
 # If the sonar.sso.groupsHeader is set, the user will belong to those groups if groups exist in SonarQube.
-# If none of the provided groups exists in SonarQube, the user won't belong to any group.
-# Note that the default group will NOT be automatically added when using SSO, it should be provided in the groups list, if needed.
+# If none of the provided groups exists in SonarQube, the user will only belong to the default group.
+# Note that the default group will always be set.
 #sonar.web.sso.groupsHeader=X-Forwarded-Groups
 
 # Interval used to know when to refresh name, email and groups.