Cannot display help without `nim` binary
```
$ nimble --help
       Tip: 1 messages have been suppressed, use --verbose to show them.
nimble.nim(2191)         setNimBin

    Error:  Unable to find `nim` binary - add to $PATH or use `--nim`
```

Until a `nim` binary is needed, there should be no need to have one - starting with help display, but also when bootstrapping a project with a locked Nim version.
