Clean-up DC Sponsorship
Clean-up DC Sponsorship

* Markdown instead of HTML
* Gold Sponsorships are sold out, too.

Signed-off-by: Nathen Harvey <nharvey@chef.io>

Former-commit-id: 7d4d3b48fd8dc99ea90f19208e464aa3784c4e68
joelaha/devopsdays-web,benjohnson77/devopsdays-web,benjohnson77/devopsdays-web,benjohnson77/devopsdays-web,masteinhauser/devopsdays-web,masteinhauser/devopsdays-web,joelaha/devopsdays-web,masteinhauser/devopsdays-web,masteinhauser/devopsdays-web,joelaha/devopsdays-web,benjohnson77/devopsdays-web,joelaha/devopsdays-web