Add User Agreement and User Resource Allotments PDFs

[troyraen]

Two new documents are being created: User Agreement and User Resource Allotments. They will be under strict change control outside this repo. When new versions are cut they will be delivered to us as PDFs. We will not render the PDFs along with the rest of the website, we will only store them in this repo and link to them from the markdown docs.

• Once we get the first versions, add them to this repo and update the markdown docs to point to them. We'll need to remove current markdown content that overlaps. Most of that current content is at https://docs.fornax.sciencecloud.nasa.gov/intro-forsc but check more thoroughly once we have the PDFs.
• We might want to point the Fornax Community Forum "Terms of Service" link to the User Agreement. Check this topic for a decision: https://discourse.fornax.sciencecloud.nasa.gov/t/terms-of-service-page-in-discourse-needs-to-be-changed/406/2.