Feature Request: Show the total number of days with commits

[Fairfarren]

Hi, I would like to suggest a new feature for git-stats: displaying the total number of days with at least one commit in the statistics output (i.e., “active days”). This would help users quickly understand their overall activity and contribution frequency.

For example, along with the existing stats like “Max a day,” it would be great to see something like “Total active days: XX” in the output.

Thank you for your great work!