add help for publish command
In the docs for skim publish, we say that it supports these options:

```
skpm publish <new-version> | major | minor | patch | premajor | preminor | prepatch | prerelease
```

but when you do `skim help publish` they are not listed and I always need to go back to the docs to check the syntax.

It would be awesome to list those in the output of `skpm help`