docs: improve explanation about body option

[NozomuIkuta]

🔗 Linked issue

#92

❓ Type of change

• 📖 Documentation (updates to the documentation, readme, or JSdoc annotations)
• 🐞 Bug fix (a non-breaking change that fixes an issue)
• 👌 Enhancement (improving an existing functionality like performance)
• ✨ New feature (a non-breaking change that adds functionality)
• 🧹 Chore (updates to the build process or auxiliary tools and libraries)
• ⚠️ Breaking change (fix or feature that would cause existing functionality to change)

📚 Description

This is a follow-up PR for #92

📝 Checklist

• I have linked an issue or discussion.
• I have updated the documentation accordingly.

[codecov]

Codecov Report

Merging #276 (feff7ea) into main (d58b961) will not change coverage.
Report is 3 commits behind head on main.
The diff coverage is n/a.

❗ Current head feff7ea differs from pull request most recent head 512ea19. Consider uploading reports for the commit 512ea19 to get more accurate results

@@           Coverage Diff           @@
##             main     #276   +/-   ##
=======================================
  Coverage   92.66%   92.66%           
=======================================
  Files           5        5           
  Lines         545      545           
  Branches      103      102    -1     
=======================================
  Hits          505      505           
  Misses         40       40           

[pi0]

Thanks!