Improve CRANE Documentation

[smpeyres]

With a growing CRANE user base, especially of experimentalists who want to model their plasma experiment's chemistry, it's becoming clear that CRANE's documentation needs to be expanded to help onboard new users with minimal 1-on-1 assistance.

I have identified several notable tasks that could significantly enhance CRANE's documentation, especially for new users.

1. Set up and basic edits to ReadTheDocs.

• [x] Set up ReadTheDocs website (Completed by @dcurreli, commit fc77a79)
• [x] Put link in repo (Completed by @smpeyres)
• [x] Flesh out "running" (Completed by @smpeyres, commit c2f0ccd)
• [ ] Flesh out "tutorials" page (see below)

2. Flesh out the tutorials on the ReadTheDocs to fully explain the setup and philosophy behind the three ZDPlasKin example used for testing, similar to ZDPlasKin's "Examples" tab on their webpage. In the future, more examples and tutorials can be added to explore different discharge types and chemical processes.

• [x] Example 1 Two-Reaction Argon (Completed by @smpeyres, commit 61b0910)
• [ ] Example 2 Argon Microdischarge
• [ ] Example 3 Nitrogen Plasma with External E-Field and Electron Density (optional)

3. (Maybe no longer be necessary with ReadTheDocs) Improve and expand the user guide. Currently has some functionality, but this is the perfect place to put what can't fit in the wiki. The non-ZDPlasKin based examples such as the Lorentz attractor and the hydrogen CRM featured in the ArXiv preprint can be included. General practical guidelines for plasma chemistry modeling should be included as well (start simple, keep units consistent, maintain quasineutrality, useful formulas, etc). Additionally, .tex file should be kept in repository along with the .pdf for easier updates down the line.

• [ ] User guide: Obtain .tex file to current user guide pdf, if possible. If not, be prepared to re-write it.
• [ ] User guide: Include various examples (ZDPlasKin, Lorentz, CRM) with extended theory/explanation.
• [ ] User guide: Practical guidelines for plasma chemistry modeling.