[develop]: Initial develop branch documentation

[gspetro-NOAA]

Describe your changes

This PR updates the Introduction and Technical Overview chapters for the develop branch. As decisions are made about pulling release changes into develop and/or migration to ufs-community, I will add additional chapters back in with appropriate updates.

Issue ticket number and link

Issue #18

Test output

No testing was performed because there are no changes to the code itself. The docs can be viewed on my fork at: https://gsp-land-offline-workflow.readthedocs.io/en/docs-dev

Checklist before requesting a review

• [X] My branch being merged is up to date with the latest develop.
• [X] I have performed a self-review of my code by examining the differences that will be merged.
• [X] I have not made any unnecessary code changes / changed any default behavior.
• [ ] My code passes the DA_IMS_test, or differences can be explained. N/A - no tests run/no tests required