Add esbuild steps with metafile output to README

[yonta]

I tried this repository and stumbled upon the need to output a metafile in the esbuild configuration.
I think it would be helpful to include this in the README.

[exoego]

I think this part in README describes that.
Do you think it is not enough?

[yonta]

Oh.
Sorry, I am using esbuild v0.19 (< v0.20), so I skipped this sentence.
I need not to skip, but I didn't notice.

[yonta]

For example, how about splitting the usages steps in the README?

1. Configure esbuild to output a metafile.
   • CLI version
   • JS version
2. Write the GitHub Actions.

The CLI version is easier than the JS version, and I've also split the esbuild configuration steps.
What do you think?

[exoego]

Added CLI version example, which I was not aware of, to README in #29

[yonta]

Thanks to update README🙌