Document recursive copying

[dominikschulz]

Fixes #676

[codecov]

Codecov Report

Merging #713 into master will increase coverage by 0.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #713      +/-   ##
==========================================
+ Coverage   64.62%   64.63%   +0.01%     
==========================================
  Files         156      156              
  Lines        8889     8891       +2     
==========================================
+ Hits         5744     5746       +2     
  Misses       2459     2459              
  Partials      686      686

Impacted Files	Coverage Δ
commands.go	92.15% <ø> (ø)	⬆️
action/copy.go	75% <100%> (+3.57%)	⬆️

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