Add user guides to the repo

Requirement from Amanda:

> I'd like for us to add our User Guide to the Help Page while we are still working on designing and implementing more help material. Rachel has made the user guide into a png and into a pdf spread for digital use. As well as a front/back version for printing... Can you look into how we would add these resources and downloadable hyperlinks?

Blocked by https://github.com/InetIntel/IODA-site-files/issues/1

Start with the Help Page implementation and inspect the resources described in this issue: the PNG, PDF spread, and front/back printable guide. Check the blocking issue #1 before proceeding; done means the appropriate guide files are available through downloadable links on the Help Page.

Written by the indexing model from the issue text.