Docs: Link to the browser support page in CONTRIBUTING.md
Docs: Link to the browser support page in CONTRIBUTING.md

Instead of duplicating the supported browsers matrix, just link to
the browser support page on jquery.com.

jquery/jquery,quiaro/request-agent,eburgos/jquery,roytoo/jquery,eburgos/jquery,roytoo/jquery,jquery/jquery,rwaldron/jquery,jquery/jquery,roytoo/jquery,eburgos/jquery,rwaldron/jquery