[WEBSITE] Include trademark attribution in footer
[WEBSITE] Include trademark attribution in footer

Descriptions of the changes in this PR:

According to http://www.apache.org/foundation/marks/pmcs#attributions, include trademark attribution in the footer.

Author: Sijie Guo <sijie@apache.org>

Reviewers: Jia Zhai <None>, Matteo Merli <mmerli@apache.org>

This closes #1502 from sijie/update_trademarks

sijie/bookkeeper,sijie/bookkeeper,ivankelly/bookkeeper,ivankelly/bookkeeper,sijie/bookkeeper,apache/bookkeeper,ivankelly/bookkeeper,sijie/bookkeeper,apache/bookkeeper,apache/bookkeeper,apache/bookkeeper,sijie/bookkeeper,sijie/bookkeeper,sijie/bookkeeper,apache/bookkeeper,apache/bookkeeper,sijie/bookkeeper