Add a note about parameter ranges when doing MEFLing with `FlowCal`

[ppreshant]

Note realistic parameters for the MEFL calibration curve in this equation
$s(fl_{rfi}) = sign(fl_{rfi}) * e^b * abs(fl_{rfi})^m$

Here's the discussion on FlowCal by @castillohair

First, make sure that your beads processing is correct. m=0.68 is highly atypical and suspicious. Ideally you would have it between 0.9 - 1.1, and these should be extremely consistent across your runs (i.e. if you got 0.92 once, you should get +/- 0.1 at most every time in the same instrument)