Documentation: document data privacy aspects of using gource

[robert-heinzmann-logmein]

This is more or less a feature request :)

When looking for a "data privacy" statement for the gource tool, I did not found a lot, besides a few closed github issues (e.g. #298).

It would be great if the documentation / README.md would contain some details on the aspect of "data privacy" and how the tool can safely be used on private repos and protecting portial personal identifyable information.