fix: links in CONTRIBUTING.md

[gcroci2]

This PR fixes issue #243 by updating two links in The Contributing Guide, CONTRIBUTING.md of the wrangling-genomics repository:

• How to Contribute to an Open Source Project on GitHub whose link was leading to a 404.
• The repository link reference which was pointing to a placeholder.

[github-actions[bot]]

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[ErinBecker]

Thank you @gcroci2 for these fixes!