Is interact() documented somewhere? #171

@doutriaux1 I have just noticed that interact is not documented in the VCS Quick Reference page, where it would fit nicely. It's probably not documented in the notebooks, where I guess it makes no sense to use interact.

I have also googled cdat vcs 'interact()' but it does not produced anything useful

The only place where I have found it, is in the Index (of the vcs documentation)

Interact is very useful for people who want to click on the canvas to check the plot values!

Oh, I have just found that I already mentioned this in CDAT/vcs#144