chore: add custom item attribute in readme

[zhu-xiaowei]

Description

1. add custom item attribute in readme

General Checklist

• Added new tests to cover change, if needed
• Build succeeds using Swift Package Manager
• All unit tests pass
• Security oriented best practices and standards are followed (e.g. using input sanitization, principle of least privilege, etc)
• Documentation update for the change if required
• PR title conforms to conventional commit style
• If breaking change, documentation/changelog update with migration instructions

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (eb441ae) 94.88% compared to head (49f2adb) 94.67%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #42      +/-   ##
==========================================
- Coverage   94.88%   94.67%   -0.21%     
==========================================
  Files          35       35              
  Lines        1935     1935              
==========================================
- Hits         1836     1832       -4     
- Misses         99      103       +4     

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