Add elfconv to CNCF landscape

[yomaytk]

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Please check each of these after submitting your pull request:

• Are you only including a repo_url if your project is 100% open source? If so, you need to pick the single best GitHub repository for your project, not a GitHub organization.
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[yomaytk]

@caniszczyk When you have a chance, could you take a look?