Update support.inn.org docs

[benlk]

The documentation at https://support.inn.org/article/100-pym-shortcode needs to be updated in the following ways:

• "There are no plugin settings" is false since version 1.3.2.1 in 2018, when we added a settings page. We can probably strike the words "There are no plugin settings, but" and start the sentence with "There are some...."
• This page should mention Gutenberg compatibility before the shortcode.
• Include a link to https://blog.apps.npr.org/pym.js/ and credit NPR somewhere on the page.

---

Discovered during #68