adding docu to mean! explain target should not alias with the source

[josemanuel22]

fix issue #71

[codecov[bot]]

Codecov Report

Merging #96 (547bf4d) into master (5256d57) will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##           master      #96   +/-   ##
=======================================
  Coverage   96.91%   96.91%           
=======================================
  Files           1        1           
  Lines         422      422           
=======================================
  Hits          409      409           
  Misses         13       13           

Impacted Files	Coverage Δ
src/Statistics.jl	96.91% <ø> (ø)

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