Example in register_plugins docs

[steveb-123]

Including a complete example in the register_plugins documentation would increase the clarity significantly.

Particularly, including a gate from flowCore here as the example would give a useful documentation link between the two packages.

[mikejiang]

here are a few https://rpubs.com/wjiang2/177022 https://rpubs.com/wjiang2/188182 https://rpubs.com/wjiang2/320381