Add examples into the NPM imports docs for when exports fail

some bundlers have special bundling powers and dont like or ignore npm exports, there should be some docs for folks importing and need direct path references.

```
@import "open-props/style";
/* would have docs for also */
@import "open-props/open-props.min.css";
```

Locate the existing NPM imports documentation and review how package imports are currently explained. Add examples for direct path references such as @import "open-props/open-props.min.css" alongside @import "open-props/style", with the guidance covering bundlers that ignore or do not support npm exports.

Written by the indexing model from the issue text.