Documentation for CESM2 release

This issue documents things needed for the cism-in-cesm documentation for the cesm2 release.

- [x] Rewrite chapter 1 (introduction) - Gunter (with help from Bill L, Bill S)

- [x] Chapter 2 (quick start) - Bill S
- Rewrite overview
- For the most part, point to CESM quick start and/or cime documentation
- Keep modifying namelist settings, rewrite as needed
- Keep modifying source code... talk about modifying in-source vs. SourceMods, and the two different places for SourceMods to go
- Point out specific things useful for LIWG
- One-way vs. two-way coupling

- [x] New chapter on developing and modifying CISM
- Add a section on directory structure (taken from current chapter 4) - Bill S
- Move the "simulating the Greenland ice sheet" section from the current chapter 4 to there - Gunter

- [x] Add a section on grids (rewritten from the section in the current chapter 4) - Bill S (with help from others)
- Point to wiki page on new CISM grid. Update 2018-05-31: Maybe move that wiki page into the user's guide... in that case, maybe make grids its own chapter.
- Note need for glacier region to be consistent in CLM: need to have virtual columns and melt_replaced_by_ice in the CISM domain

- [x] Chapter 3 (TG compsets) - Bill S

- [ ] Chapter 4 (the dynamic ice sheet model) - Gunter
- May cut the description of the dynamic ice sheet model (4.1) entirely, just pointing to the full CISM documentation
- However, we want to keep the "coupling to CLM" section, but move this to a separate chapter (see below)
- Also keep description of different directories, but move to quick start guide (Bill S)
- Keep some description of time steps - Gunter

- [x] Chapter 5 (ice sheets in the community land model, and coupling) - Bill L with help from Bill S
- Rework what's there, and/or point to CLM documentation
- Include remapping between CISM and CLM - Bill L
- Add other fields sent from CISM - Bill S / Bill L

- [x] Chapter 6 (FAQ) - cut this for now; can add things back in later as needed (note that they'll need documentation for the new code)
- But see below: move some of this into a new chapter on output

- [x] New chapter on controlling output from cism and clm
- Add a section on input/output (rewritten from the section in the current chapter 4) - Bill S
- Move the old 6.7 and 6.8 here

- [x] Chapter 7 (acknowledgements) - Bill L

- [ ] Chapter 8 (references) - Gunter and Bill L

----

Other things we want to mention somewhere:

- [x] Need to set restart=0 when doing a hybrid run where you have changed cisminputfile to point to a restart file from a standalone case, or a case with different physics (Laura Muntjewerf's issue August, 2018)