No fallback to `main` when no master branch exists.

New user here. When starting work on a project that uses `main` as the main branch name, there is no help or fallback for this error:

```
$ git appraise request
fatal: 'refs/heads/master' - not a valid ref
```

I had to read the code to figure out that `-target` is the needed option, but, that should really be a fallback mechanism, or, alternatively, the error comment should tell me that if I want this by default, I can do this through a specified (full example as best as possible) `git config` command to make this the default for this repo.