Update contributing doc link bodies to gz from ign

[tfoote]

Summary

Update contributing guide to use new verbiage

Checklist

• [x] Signed all commits for DCO
• [na] Added tests
• [x] Updated documentation (as needed)
• [na] Updated migration guide (as needed)
• [na] Consider updating Python bindings (if the library has them)
• [na] codecheck passed (See contributing)
• [na] All tests passed (See test coverage)
• [x] While waiting for a review on your PR, please help review another open pull request to support the maintainers

Note to maintainers: Remember to use Squash-Merge and edit the commit message to match the pull request summary while retaining Signed-off-by messages.