Make new page for newsletter

[kevinsimper]

There should be a page that describes the newsletter and contains the newsletter form. It should be on /newsletter.

[jawkha]

@kevinsimper I'll work on this one too but I'll need help with the content.

[kevinsimper]

@abdualrhman just submitted a PR in #8

If you will review it I would appreciate the help! @jawkha 👍

[jawkha]

@kevinsimper #8 looks alright but I want to merge it locally and see how it works. For this, I think you have to give me the right permissions.