chore: add pip reference for Flags in transaction data

[kehiy]

Description

added the pip reference of Flags in transaction data.

[codecov]

Codecov Report

Merging #675 (b5714e0) into main (85f3063) will increase coverage by 0.02%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main     #675      +/-   ##
==========================================
+ Coverage   83.70%   83.72%   +0.02%     
==========================================
  Files         167      167              
  Lines        8008     8008              
==========================================
+ Hits         6703     6705       +2     
+ Misses       1002     1001       -1     
+ Partials      303      302       -1     

[themantre]

We have referenced PIP in the PR #671
The comments in the code should primarily focus on providing information about the code itself, rather than referencing external resources.
Thank you for your understanding.