Acknowledge .NET limitation when appending to existing ZipArchive

[santisq]

Solves #38. Adds a Note to README, New-ZipEntry, Compress-ZipArchive and Set-ZipEntryContent.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.96%. Comparing base (d756553) to head (034d258).
Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #44   +/-   ##
=======================================
  Coverage   90.96%   90.96%           
=======================================
  Files          55       55           
  Lines        1826     1826           
  Branches      215      215           
=======================================
  Hits         1661     1661           
  Misses        134      134           
  Partials       31       31           

Flag	Coverage Δ
PS_5.1	90.96% <ø> (ø)
PS_7_Linux	90.63% <ø> (ø)
PS_7_Windows	90.96% <ø> (ø)

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