Add comment including videoio library

[Adimote]

I keep forgetting what library I need to include on my laptop to get my opencv bindings to work, as I'm running a later version where video IO tasks have been split into a separate library.

Add a comment which indicates what you must do to get it to work.

[kierdavis]

I wonder if this can be made into an automatic test (e.g. by checking the version of opencv with pkg-config)

[RealOrangeOne]

We should check if this causes issues on older versions of opencv. Perhaps we can just install it by default, and installs which need is will just use it, and those who don't, don't.

[PeterJCLaw]

I think the issue is that videoio doesn't exist as a separate library in earlier versions.