feat: add jp functions docs

[eddycharly]

Explanation

Add jp functions docs.

[codecov]

Codecov Report

Attention: Patch coverage is 90.90909% with 1 line in your changes missing coverage. Please review.

Project coverage is 24.59%. Comparing base (790f57d) to head (2cf0a80).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
pkg/jp/functions/at.go	50.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #527      +/-   ##
==========================================
+ Coverage   24.54%   24.59%   +0.05%     
==========================================
  Files          92       92              
  Lines        4348     4351       +3     
==========================================
+ Hits         1067     1070       +3     
  Misses       3171     3171              
  Partials      110      110              

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