Update documentation for basic usage

[rljacob]

Update the documentation for the basic usage of CCS. Define more key concepts. Add table for compset alias one-letter case names. Make sure files created after create_newcase and ./case.setup match current function. Change titles of two major sections to be about using CCS and configuring CCS.

Test suite: build locally using sphinx. Test baseline: N/A Test namelist changes: N/A Test status: bit for bit

User interface changes?: N

Update gh-pages html Y.

[rljacob]

This is just to get things in shape for the E3SM tutorial. More cleanup is needed.

[github-actions[bot]]

You can preview documentation at https://esmci.github.io/cime/branch/rljacob/docs/tutorial-prep/html/index.html

[rljacob]

Merging so its live for tutorial starting in a few minutes.