updating setorder.Rd

[MichaelChirico]

Related to #2572 (point 3)

I may have gone overboard with the radix sort references 🤷‍♂️

[codecov]

Codecov Report

Merging #3389 into master will decrease coverage by <.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #3389      +/-   ##
==========================================
- Coverage   95.09%   95.09%   -0.01%     
==========================================
  Files          65       65              
  Lines       12122    12120       -2     
==========================================
- Hits        11528    11526       -2     
  Misses        594      594

Impacted Files	Coverage Δ
R/foverlaps.R	100% <0%> (ø)	⬆️

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[codecov]

Codecov Report

Merging #3389 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #3389   +/-   ##
=======================================
  Coverage   95.09%   95.09%           
=======================================
  Files          65       65           
  Lines       12120    12120           
=======================================
  Hits        11526    11526           
  Misses        594      594

---

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Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 267e314...ca5098f. Read the comment docs.

[mattdowle]

Nice edit. Much clearer. The youtube video was a bit too much about LSD integers. I replaced that with Terdiman and Herf links (repeated from ?setkey).
?setkey description looks a bit out-of-date too I noticed (I added a new point 4 to #2572 for that).