Explore possible ways for a "Help" button or "Intro" to FSH Online to work

Transferred from internal JIRA issue originally created 2021-05-10.

Possible ideas that have been discussed:

* Static overlay of tooltip/blurbs that point out different areas of the app and what each section/button does
* An interactive introduction to the tool that walks through step by step the basic workflow of the tool. This could include steps that say "Enter the following example FSH: ..." and could point to "Click the 'Convert to JSON' button".
* A simple modal dialog with instructions for how to use the tool
* A page in FSH School that documents FSH Online