add info for unused index.html

Author: jetzlstorfer

Diff for: _index.html

@@ -3,8 +3,11 @@
 ---
 
 <!--
+  ATTENTION
   if index.html should be enabled, it has to be named
   index.html instead of _index.html
+
+  In this case the permalink in about.md sets abouts.md as the index page
 -->
 
 <div class="posts">