Webmention hex sticker

[aaronpk]

Feedback from IRC:

• "Webmention looks like a weird 90s techno flower"
• text should be horizontal to match the rest

[tantek]

Consider using: https://indieweb.org/File:webmention-logo.svg and horizontal "Webmention" underneath it, same horizontal alignment as others.

OR change it to use a hex version of https://pbs.twimg.com/profile_images/719410954497200128/rXuEEpQu_400x400.jpg along with "Webmention.rocks" as the text underneath