P3 fall speed regime docs

[rorlija1]

Purpose

To-do

• see the many TODOs in the docs!
• and a little note in the P3SchemePlots.jl about parameters I haven't computed

Content

• draft of docs
• some parameters listed in P3SchemePlots.jl

---

• I have read and checked the items on the review checklist.

[codecov]

Codecov Report

Patch and project coverage have no change.

Comparison is base (0519c40) 98.19% compared to head (3cda712) 98.19%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #191   +/-   ##
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  Coverage   98.19%   98.19%           
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  Files          13       13           
  Lines         887      887           
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  Hits          871      871           
  Misses         16       16           

Files Changed	Coverage Δ
src/Parameters.jl	53.84% <ø> (ø)

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[trontrytel]

Closing this one. We will try to use the Chen 2022 velocities