Add favicon <link> snippet

[psolbach]

Might be a good idea to add the proper <link> tag as outlined by the HTML5 specification anywhere tied to responses or just as an indicator that this is possible for users who place their own favicons here. Just tested this on Chrome, redirects are resolved by the User Agent here. But we should try this across all major Browsers to be sure.

e.g.

<link rel=icon href=https://iconbin.com/api/messenger.com/src sizes="500x500" type="image/png">
<link rel=icon href=https://iconbin.com/api/twitter.com/src sizes="any" type="image/svg+xml">