docs: add G116 rule description to README

[kfess]

Description

Add missing G116 rule description to README's Available rules section.
The G116 rule was added in #1431 but the README was not updated.

Sorry for forgetting to include this in #1431.

[codecov-commenter]

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Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 64.54%. Comparing base (1216c9b) to head (63c3065).
⚠️ Report is 143 commits behind head on master.
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Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1439      +/-   ##
==========================================
- Coverage   68.49%   64.54%   -3.96%     
==========================================
  Files          75       78       +3     
  Lines        4384     4716     +332     
==========================================
+ Hits         3003     3044      +41     
- Misses       1233     1524     +291     
  Partials      148      148              

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