Fix packaging in ESM environment

[Holi0317]

Hello 👋🏽

This package cannot be imported in ESM environment even it says it should work in package.json.
For example, if the downstream consumer has type: "module" in their package.json, the import will fail with ERR_MODULE_NOT_FOUND when the entry tries to resolve internal modules:

This can be solved by adding .js suffix to the import path and specify moduleResolution to node16 in tsconfig to enforce this rule.

I am also adding a ESM-only warning in the README, copied from https://github.com/remarkjs/remark-directive because it seems the remark plugin ecosystem is pretty much ESM-only now.
But I am not sure if this package will work in deno or in the browser, through esm.sh so I didn't copy those instruction over.

After the change, the build passes arethetypeswrong check.

Before	After

Some reference reading for this ESM issue:

• https://blog.isquaredsoftware.com/2023/08/esm-modernization-lessons/
• https://www.typescriptlang.org/docs/handbook/modules/reference.html#node16-nodenext-1
• https://gist.github.com/sindresorhus/a39789f98801d908bbc7ff3ecc99d99c

[myl7]

Included in v2.1.2

Thanks for the catch and enclosed standard ESM packaging method!

I would later check all my other JS/TS packages with the tool arethetypeswrong.

[Holi0317]

Thanks a lot!

ESM is really a hard problem in JS ecosystem now hahaha.