Add video to commutator plugin

[cjsha]

Per tech talk 2025-07-16:

An example video would be helpful to understand what the commutator plugin does. This is particularly important for this plugin because there is no in-GUI indication of what this plugin does because it drives behavior of external hardware.

Here's a proper example video: https://open-ephys.org/acq-board#SPI-commutator

[ChucklesOnGitHub]

And link out to the relevant tutorials: https://open-ephys.github.io/acq-board-docs/Tutorials/Commutator.html

Consider this discussion re: an onix oe gui commutator tutorial open-ephys/commutator-docs#42