Standardize/agree on shapes for design docs

[lwjohnst86]

I've used https://venngage.com/blog/flowchart-symbols/

There's also the ISO 5807 https://www.useworkspace.dk/en/blog/iso-5807-flowchart-symbols-guide and https://cdn.standards.iteh.ai/samples/11955/1b7dd254a2a54fd7a89d616dc0570e18/ISO-5807-1985.pdf