Docs Update: Tutorials Folder and Running on ReadTheDocs

[smpeyres]

1. I created a directory called "tutorials" that at the moment contains some material from tests and problems on the two reaction argon and microdischarge, respectively. Thought this would be an appropriate place to store all files required for running the tutorials as directed on the future ReadTheDocs pages.
2. Removed .txt files from gitignore file since they are used everywhere, but a proper workaround to avoid .txt garbarge could be put in place.
3. Early version of running tab on ReadTheDocs.