Add notes about Lenia CA

[jasonwebb]

Add some sort of reference about Lenia, a 2D CA with continuous space, time, and states from Bert Chan. This may be a large + interesting enough system to warrant a dedicated section that references the CA section.

Figure out what it has in common with and differs from SmoothLife.

Important links:

• Lenia - Biology of Artificial Life - original 2019 paper by Bert Wang-Chak Chan
• Bert's source repo - https://github.com/Chakazul/Lenia
• Showcase video - https://vimeo.com/277328815