Add option to log modified files about addlicense

[x1ddos]

+1 to option 2, a flag. only I would make it -v, as in "verbose". WDYT? Happy to review a change.

Re: exit code. It definitely makes sense for gofmt because it's always clear what the desired outcome is: code is formatted appropriately.

But here it isn't as clear what the desire is imho. Both "no files modified" and "at least one file modified" can be an ok expectation. Additionally, it would be confusing when addlicense exits with non-zero code due to say an I/O error.

We could of course add and document different exit codes for different scenarios but it still isn't clear when you're just checking for non-zero.

Also, nothing prevents us from adding both exit codes and a flag but I would definitely start with the latter and see whether it's sufficient.

[tweksteen]

Agreed. Sent #25 for review.

[x1ddos]

This is resolved by #25