Create an OPE user guide to author new books

[DanNiESh]

Working on the repos re-org of OPE project under https://github.com/OPEFFORT. Current repos are still private. Will create a user guide for using OPE CLI tool to seed new books and then make repos public to all.

[IsaiahStapleton]

The User Guide is now live at: https://isaiahstapleton.github.io/ope-project/user_guide/user_guide_intro.html