Can something be printed when doing a git diff to show that nbdime is running?

[himat]

Can something be printed when doing a git diff to show that nbdime is running? Because when I do a git diff with a few changed notebooks, the git diff hangs for 20 seconds before showing the output. So it would be useful to know that it's nbdime taking this long and not something else. So when git diff is run, it would be good if it just printed out something like nbdime running... before replacing it with the diff text.

[vidartf]

Since the output is passed through git, I'm not sure if this is something that can be reliably done or not. If someone has time to test that would be welcome. Another solution would of course be to make the diffs run faster, so if you have some notebooks that are systematically slow, please consider sharing so we can put it in the repo as a profiling/test case to optimize against!