Improve README search positioning

[codeforester]

Summary

• Reposition the README opener around searchable Bash standard library language.
• Keep the Base extraction context while making independent Homebrew, source checkout, vendored, and submodule consumption clear.
• Name the existing helper areas directly so readers and search indexing see the project scope sooner.

Issue

Closes #66

Validation

• git diff --check origin/main...HEAD

Notes

Documentation-only README positioning change; no runtime behavior or release metadata changes.

Checklist

• Branch name follows <category>/<issue>-<YYYYMMDD>-<slug>.
• Pull request is scoped to one issue, unless a documented multi-issue exception applies.
• Pull request body explains what changed and how it was validated.
• Relevant project checks pass.
• Documentation is updated when behavior or user-facing commands change.
• CHANGELOG is updated for notable user-visible or release-worthy changes. Not applicable: README positioning only.
• Pull request includes Fixes #<issue> or Closes #<issue> when merge should close the issue.