[Docs] Touch Ups to TwoReactionArgon

[smpeyres]

Small pull-request, but following was done as discussed:

• @ananthanarasimhanj pointed out error in simulation conditions table (wrong ionization coeff value) and problems with spline usage Interpolation #104 and reaction order Order of the reactions with the usage of EEDF #103. Error was fixed, spline was switched to linear, and warning was made for reaction order.
• Re-ran input file with linear interpolation due to change of ionization rate coefficient.
• Split the input file into chunks with accompanied text, rather than whole input file at top.
• Added plasma density growth prediction to theory section and updated figure to show both initial rise prediction and steady state prediction with annotations, similar to ZDPlasKin.
• Renaming of files for consistency and clarity.
• Outline of ArgonMicrodischarge.rst (will be fleshed out next)

[dcurreli]

Looks good