Added note to README about implementing modules' responsibility to uninstall their own variables.

README.txt

@@ -32,7 +32,10 @@ Checklists are declared as multidimensional arrays using
 hook_checklistapi_checklist_info(). They can be altered using
 hook_checklistapi_checklist_info_alter(). Checklist API handles creation of menu
 items and permissions. Progress details are saved in one Drupal variable per
-checklist. See checklistapi.api.php for more details.
+checklist. (Note: it is the responsibility of implementing modules to remove
+their own variables on hook_uninstall().)
+
+See checklistapi.api.php for more details.
 
 
 TODO