Update the description for chemsys_permutations

[acrutt]

Update the description for chemsys_permutations because the previous description was inaccurate

[codecov-commenter]

Codecov Report

Merging #424 (509b6ce) into main (371576f) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #424   +/-   ##
=======================================
  Coverage   98.06%   98.06%           
=======================================
  Files         109      109           
  Lines       23205    23205           
=======================================
  Hits        22755    22755           
  Misses        450      450           

Impacted Files	Coverage Δ
emmet-builders/emmet/builders/utils.py	100.00% <ø> (ø)

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[munrojm]

Thanks @acrutt!