[Lazarus revival] add Github Access Structure Overview section

[kax168]

Maintainer Briefing: add Github Access Structure Overview section

What this PR was trying to do

Document the proposed GitHub permission hierarchy for Technical Committee members, Project Captains, Committers, and Triagers across the Express, jshttp, and pillarjs organizations.

What changed in the repo since it died

The repository has changed substantially since the original PR, including removal of Contributing.md, documentation updates, dependency upgrades, fixes, features, and CI changes. The original target location and governance links therefore required adaptation.

What Lazarus changed to revive it

Rebased the four original commits onto current master while preserving Jon Church’s authorship. Moved the 29-line access overview to Readme.md and updated the governance, organization, and Triager Guide links. The revived branch merges cleanly.

Test evidence

Evidence	Before	After
Tests detected	Yes	Yes
Test command	npm test	npm test
Tests passed	No	Yes
Merge clean	No	Yes

Risk assessment

This is documentation-only, but it describes organization-wide security and governance policy. The original author characterized the definitions as personal opinions and specifically questioned Committer scope; evidence confirming that these roles and permissions are current policy is unavailable. Post-revival validation reports npm run lint passing and npm test passing with 1,260 tests.

Credits

Originally contributed by @jonchurch.

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Original PR: expressjs#5503
Original author: @jonchurch