Add Tippy for tooltips

[stevepiercy]

Tippy would be helpful to preview link content, such as Glossary terms, before clicking the link.

https://sphinx-tippy.readthedocs.io/en/latest/

Refs:

• Show tooltips in text for glossary terms and permalinks for definitions documentation#1499
• Show tooltips in text for glossary terms and permalinks for definitions training#540

[Manas-Kenge]

Hey @stevepiercy I have setup tippy locally and it works. Currently it looks something like this. This only works for internal links though. For something like [Plone Contributor Agreement](https://plone.org/foundation/contributors-agreement). it doesn't show the tooltip.