Include Earthly as a related tool

[ryuheechul]

Include Earthly as a related tool as I find the usages could overlap between two tools.

The description is simply copied from https://github.com/earthly/earthly.

Feel free to modify this PR by either:

• adding more commit
• create another PR to replace this and close this one
• ask me to make changes

Status: Ready

[stepchowfun]

Hi @ryuheechul, thanks for creating this pull request!

Earthly is a CI/CD framework that allows you to develop pipelines locally and run them anywhere. Earthly leverages containers for the execution of pipelines. This makes them self-contained, repeatable, portable and parallel.

This seems more like an ad than a meaningful comparison. It doesn't mention the relative strengths or weaknesses of the two tools, so I don't think it actually helps people make a decision either way.

I do think it would be valuable to have a concise summary of the differences between these tools, since they do overlap quite a bit as you mentioned. But a little more investigation would be needed before I can merge this pull request.

[ryuheechul]

@stepchowfun I agree and sounds good to me! 👍🏼