Add more description to the extra options parameters

[greglucas]

Currently, the options descriptions are taken from the Fortran source. This is somewhat cryptic and requires more advanced knowledge of the code to understand what some of them mean. It would be helpful to describe these in a little bit more detail for the average user of the code without needing to trace through any source code.

• Update docstring text

  pymsis/pymsis/msis.py

  Lines 278 to 306 in cdd4043

  	f107 : float
  	Account for F10.7 variations
  	time_independent : float
  	Account for time variations
  	symmetrical_annual : float
  	Account for symmetrical annual variations
  	symmetrical_semiannual : float
  	Account for symmetrical semiannual variations
  	asymmetrical_annual : float
  	Account for asymmetrical annual variations
  	asymmetrical_semiannual : float
  	Account for asymmetrical semiannual variations
  	diurnal : float
  	Account for diurnal variations
  	semidiurnal : float
  	Account for semidiurnal variations
  	geomagnetic_activity : float
  	Account for geomagnetic activity
  	(1 = Daily Ap mode, -1 = Storm-time Ap mode)
  	all_ut_effects : float
  	Account for all UT/longitudinal effects
  	longitudinal : float
  	Account for longitudinal effects
  	mixed_ut_long : float
  	Account for UT and mixed UT/longitudinal effects
  	mixed_ap_ut_long : float
  	Account for mixed Ap, UT, and longitudinal effects
  	terdiurnal : float
  	Account for terdiurnal variations

• Provide examples of turning each parameter on/off and what that looks like visually