Make Newsletter a link in footer

There was a user today in the irc asking where they can join to be notified of new Gitlab omnibus releases. It is currently in the contact page, but I believe there should be also a Newsletter link in the footer. Let me know what you think, I can craft an MR.

It's also in the bottom of every blog post. But I'm okay with it. Everything that makes people subscribe to the newsletter is great!

Milestone removed

Milestone changed to Marketing

Status changed to closed