Update Readme to include basic full example.

[aw-creative]

Gitchangelog is not saving to an output file.

Running gitchangelog for the first time. Using the examples provided in your documentation
no changelog is created.

Can you add a super basic tutorial in the readme on creating a changelogs and outputting the file., its unclear how to do this currently.

I can get it to display the generated change-log in the terminal window, but it will not output to a file.

[ElijahAhianyo]

its 2020 and im facing the same issue as well, the examples stated don't output to a file

[ghost]

its 2021 and i'm facing the same issue as well, the examples stated don't output to a file