Develop a solution to surface gitbook styleguide in Joplin

### As a content author I want to see the relevant style guide pages in Joplin so that it is easier to adhere to adjust to writing for residents.

**Is your feature request related to a problem? Please describe.**
As shown in this slack thread, we've realized that an old non-gitbook guide is what is currently surfacing in Joplin. Gitbook was chosen as the style guide platform because it is easy to update, so we want to stick with that platform. The problem is gitbook doesn't allow for embedding its content in iframes.

https://austininnovation.slack.com/archives/C8T4YD23T/p1594226897026100

**Describe the solution you'd like**
Not sure what is best, but it seems like there is a few options.