Fix formatting in Grouping docstring

[likanzhan]

No description provided.

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (main@365e5f7). Click here to learn what that means.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #511   +/-   ##
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  Coverage        ?   94.14%           
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  Files           ?       26           
  Lines           ?     2239           
  Branches        ?        0           
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  Hits            ?     2108           
  Misses          ?      131           
  Partials        ?        0           

Impacted Files	Coverage Δ
src/grouping.jl	100.00% <ø> (ø)

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[palday]

thanks!