message: Adds mailto for contact us link
diff: li Custom profile bio
  .premium-tiers__tier.premium-tiers__tier--enterprise
  .premium-tiers__tier__title Enterprise
  - .premium-tiers__tier__price.selectable: strong Contact Us
  + a.premium-tiers__tier__price.selectable( href='mailto:info@are.na' )
  + strong Contact Us
  .premium-tiers__tier__includes Are.na + Premium +
  ul.premium-tiers__tier__features
  li Custom Domains
  