docs: add usage workflow and fix blog links

[Dafenxz0]

Hi! This addresses two of the rough edges from #19:

• adds a concrete example workflow so a new user can see when recon, propose, preflight, and triage fit into a contribution
• updates the two blog links from the old JFrog URLs, which now return 404, to the current Tessl blog URLs

I also added a short changelog note so the docs change is visible in the release history.

Validation:

• git diff --check
• curl -I -L on both updated Tessl blog URLs returns 200
• Tried python tests/test_github_sh_envelope.py --repo tesslio/good-oss-citizen --issue-number 13 --pr-number 12 --file-path README.md, but it cannot run in this Windows environment because the script goes through bash/WSL and WSL has no distro installed here. This is docs-only and CI should run the smoke test on Ubuntu.

AI disclosure: I used Codex to inspect the repo, update the README/changelog, and run the validation above. I reviewed the diff before opening the PR.

Closes #19