Clarify licensing

Author: tomas-abrahamsson

COPYING.LIB

@@ -1,7 +1,13 @@
 NOTE! It is ok to link this library with code covered by
-the Erlang public license, http://www.erlang.org/EPLICENSE
+other licenses, such as the Apache License Version 2.0, that the
+Erlang/OTP system uses, as well as other licenses.
 
-NOTE! This license does not cover the code generated by gpb.
+NOTE! This license does not cover the code generated by gpb. The code
+generated by gpb is owned by the owner of the input files used when
+generating it.
+
+NOTE! The files in the priv/proto3/google/protobuf/ sub directory
+are not covered by this license.
 
 /Tomas Abrahamsson