Add diagrams for minimal examples in wiki and liboqs documentation

[anvega]

I've created Mermaid diagrams for the two minimal examples currently in the liboqs wiki and the examples on the docs site. These aim to enhance the understanding of the key encapsulation and digital signature processes.

• Initially discussed on Discord (conversation summary attached below)
• The wiki isn't directly in the project repository, making direct contributions challenging
• There's interest in incorporating these diagrams into the documentation

Proposal:

1. I'd like to have these reviewed for which I'll file a PR to the site repo
2. Once reviewed and approved, consider adding them to the wiki as well

I'll share the code for these diagrams. The way it's rendered in the wiki of my fork. GitHub can render this directly from markdown, but I can also provide PNG exports if preferred.

Questions:

1. What's the preferred format for submitting these diagrams? (Mermaid code, PNG, or both?)
2. Are there any specific style guidelines I should follow for consistency with existing documentation?
3. Where in the docs would these diagrams be most beneficial?

I'm happy to submit a PR to contribute these diagrams to the project once I have some guidance on the above questions.