Add link to GitHub Action

[rossmacarthur]

Just wanted to share the GitHub Action I wrote to install just. I use just regularly as a command runner in my projects and often want to run it in CI. See extractions/setup-just.

[casey]

This is awesome!

For the readme, what do you think about:

=== GitHub Actions

link:https://github.com/extractions/setup-just[extractions/setup-just] can be used to install `just` in a GitHub Actions workflow.

Example usage:

```yaml
- uses: extractions/setup-just@v1
  with:
    just-version: 0.8  # optional semver specification, otherwise latest
```

[casey]

Is "semver specification" the word for a semver requirement specifier, i.e. "^0.5.0"?

I was trying to figure out what people call it most frequently, but nothing stood out. It seems like, in practice, people don't distinguish between a semantic version, e.g. 0.5.0, and a npm-style semver specifier, i.e ^0.5.0.

In any case, semver specification is fine.

[rossmacarthur]

Happy with your requested changes to the text, I have updated the branch.

Yes, it is a semver requirement specifier. I'm using this package in the GitHub Action: https://www.npmjs.com/package/semver. This package resolves plain versions slightly differently to Cargo though where 0.5.0 is equivalent to =0.5.0 not ^0.5.0.

[casey]

Awesome, merged.

You might consider documenting in the action's readme that it's an npm-style semver spec. Just users are pretty varied, but I think a good chunk of them are Rust users, and they might be confused by the difference.

Thanks so much for writing and documenting this, I think it's a really nice addition.