Announce the tails-ux mailing-list

Once related blocking tasks will be done, we will have to publicise the mailing-list by writing a blog post on the website (and maybe other actions ?)

Related issues

Is duplicate of #7743 (closed)

Original created by @tchou on 7744 (Redmine)

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information