contributing docs

[maryliag]

add documentation on how to contrib/use. Make improvements on existing workflows

[Copilot]

Pull request overview

This PR adds contributor-facing documentation to the shared-workflows repository and makes incremental improvements to the existing security workflows. It introduces a top-level CONTRIBUTING.md and a .github/workflows/README.md that explain the two supported workflow shapes (reusable uses:-style vs. centrally-executed), wires a workflows catalog table into the main README.md, and hardens the zizmor, codeql, and scorecard workflows with job names, concurrency controls, and clearer permission comments. The zizmor workflow is also made reusable via workflow_call with usage documentation.

Changes:

• Adds CONTRIBUTING.md and .github/workflows/README.md documenting the contribution process and workflow layout conventions; adds a workflows catalog table to README.md.
• Makes zizmor.yml a reusable workflow (workflow_call), adds a usage header comment, sets persona: pedantic, and adds job naming/concurrency.
• Adds concurrency groups and job names to codeql.yml and scorecard.yml, and inlines permission-rationale comments.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
README.md	Adds a link to CONTRIBUTING.md and a Workflows catalog table listing the reusable Zizmor workflow.
CONTRIBUTING.md	New guide covering proposing/using shared workflows, layout conventions, and code ownership.
.github/workflows/README.md	New directory README explaining the two workflow shapes and where supporting files live.
.github/workflows/zizmor.yml	Adds workflow_call, usage header, concurrency, job name, and persona: pedantic.
.github/workflows/codeql.yml	Adds a job-level concurrency group (collides across matrix entries — see comment).
.github/workflows/scorecard.yml	Adds job name, concurrency, and consolidates permission comments.

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[trask]

thanks!