Improve documentation regarding header types

Change-Id: I4b6f15c0606c86c8ec000d69a479e4ee72a4cba9
diff --git a/script/tei2korapxml b/script/tei2korapxml
index 2d1a6bf..10a2787 100755
--- a/script/tei2korapxml
+++ b/script/tei2korapxml
@@ -446,6 +446,11 @@
 C<.> should not be seperated from their predecessor token).
 (see also code section C<~ whitespace handling ~> in C<script/tei2korapxml>).
 
+=item
+
+Header types, like C<E<lt>idsHeader [...] type="document" [...] E<gt>>
+need to be defined in the same line as the header tag.
+
 =back
 
 =head2 Notes on the output