APPS-1484 Update docs for parallel-write flag

[filkeith]

• updated description

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 82.35294% with 3 lines in your changes missing coverage. Please review.

Project coverage is 78.12%. Comparing base (52d59e9) to head (ded333d).
Report is 1 commits behind head on xdr-support.

Files with missing lines	Patch %	Lines
cmd/internal/app/validation.go	0.00%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@               Coverage Diff               @@
##           xdr-support     #209      +/-   ##
===============================================
+ Coverage        78.11%   78.12%   +0.01%     
===============================================
  Files              109      109              
  Lines             9828     9838      +10     
===============================================
+ Hits              7677     7686       +9     
  Misses            1649     1649              
- Partials           502      503       +1     

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