clarify that bits headers are included as public headers

COPYRIGHT

@@ -78,12 +78,12 @@ All other files which have no copyright comments are original works
 Copyright © 2005-2012 Rich Felker, the main author of this library.
 The decision to exclude such comments is intentional, as it should be
 possible to carry around the complete source code on tiny storage
-media. All public header files (include/*) should be treated as Public
-Domain as they intentionally contain no content which can be covered
-by copyright. Some source modules may fall in this category as well.
-If you believe that a file is so trivial that it should be in the
-Public Domain, please contact me and, if I agree, I will explicitly
-release it from copyright.
+media. All public header files (include/* and arch/*/bits/*) should be
+treated as Public Domain as they intentionally contain no content
+which can be covered by copyright. Some source modules may fall in
+this category as well. If you believe that a file is so trivial that
+it should be in the Public Domain, please contact me and, if I agree,
+I will explicitly release it from copyright.
 
 The following files are trivial, in my opinion not copyrightable in
 the first place, and hereby explicitly released to the Public Domain: