Clarify steps required to create an NPM module

In following the directions in the ["Steps"](https://github.com/denoland/dnt#setup) section I get the following error after running `npm publish`:

```
npm ERR! code ENEEDAUTH
npm ERR! need auth This command requires you to be logged in to https://registry.npmjs.org/
npm ERR! need auth You need to authorize this machine using `npm adduser`

npm ERR! A complete log of this run can be found in: /Users/adamzerner/.npm/_logs/2024-02-02T07_19_33_940Z-debug-0.log
```

It looks like there are more steps to complete. I think that it would be helpful for `dnt`'s docs to mention this, and perhaps link to a place where these steps are documented.