Add language about rights given by posting a patch:

Add language about rights given by posting a patch:

    <li>PostgreSQL is licensed under a BSD license.  By posting a patch
    to the public PostgreSQL mailling lists, you are giving the PostgreSQL
    Global Development Group the non-revokable right to distribute your
    patch under the BSD license.  If you use code that is available under
    some other license that is BSD compatible (eg. public domain), please
    note that in your email submission.</li>