Document GitHub usernames in PackageInfo

[lgoettgens]

Summary

Document the optional GitHubUsername field in the Persons records of PackageInfo.g and add the known GitHub username for the current Example package maintainer.

This addresses gap-system/gap#4784 by making the package template show where maintainers can expose GitHub usernames for automation that needs to mention them in GitHub comments. This should be merged if and only if gap-system/gap#6497 gets merged.

Created using Codex codex@openai.com

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 62.09%. Comparing base (3b57b47) to head (c352e82).

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #56      +/-   ##
==========================================
+ Coverage   62.06%   62.09%   +0.02%     
==========================================
  Files           4        3       -1     
  Lines         203      153      -50     
==========================================
- Hits          126       95      -31     
+ Misses         77       58      -19     

see 1 file with indirect coverage changes

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.