PleromaAndOutsideSites
Sometimes there's an outside site you'd like your Pleroma instance to work with, but you need some Pleroma-specific information to get it to work. Hopefully this page will eventually cover enough use cases where you'll be able to see what might be different in the Pleroma world that could get things to work for you.
Fediverse.Observer
Site Description not Showing at F.O
fediverse.observer looks for site descriptions in either the site's nodeinfo or in the meta tags in the site's index page. Apparently Pleroma's nodeinfo isn't quite the same as the spec F.O is expecting, so, the other option is to edit the index page code.
If you're running pleroma-fe, simply find your index.html (could be in your instance/static/frontends/plerome-fe/version path), and edit the line of text in it. After the <head> tag, add in <meta name='description' content="This is the description of my instance."> and that should take care of it.