Docs: link to notebooks showing how to use pyvo

The documentation and/or the README could link to notebooks showing pyvo in action. The NAVO notebooks are [rendered as html](https://nasa-navo.github.io/navo-workshop) and available in [this repository ](https://github.com/NASA-NAVO/navo-workshop).

My recommendation is to link to these notebooks rather than to copy them into an examples subdirectory in the pyvo repository.

Review the README and documentation link sections to find the appropriate place for examples. Add links to the rendered NAVO notebooks and their repository rather than copying notebooks into pyvo. Done means readers can reach both notebook resources from the documentation.

Written by the indexing model from the issue text.