posibility to set the commit id

Hey,

I really like your package!
Is there a way to set the commit ID directly.

Reason is that I do the apv commands inside a docker image what is not containing the git information.

```
RUN npm install appversion -g \
&& apv init \
&& apv set-version 1.0.$BUILD_ID \
&& apv update commit \
&& apv update build
```

Start with the `apv update commit` entry point used after `apv set-version` in the Docker command shown. Check how the command obtains Git metadata and whether a direct commit ID can be supplied without repository information. Done means the Docker workflow accepts an explicit commit ID and its behavior is covered or documented.

Written by the indexing model from the issue text.