contributing: Update contributing page
contributing: Update contributing page

Summary: * update contributing page so it doesn't say we're volunteer-driven

Test Plan: make lint test

Reviewers: anu, rschlussel, mf186042

Reviewed By: mf186042

Subscribers: mf186042

Differential Revision: https://phabricator.td.teradata.com/D756

Svjard/presto-admin,prestodb/presto-admin,prestodb/presto-admin,Svjard/presto-admin