Import wiki from original Darglint

[akaihola]

Fixes #3 partially.

Bringing in the Wiki documents and images from the Design section of the original Darglint wiki.

To do:

• move the documents to the docs/ folder
• build Graphviz images into PNG SVG as part of documentation build
• decide whether to include those PNG SVG images in the repository or to host them from somewhere else
• implement decided storage for the PNG SVG images

[real-yfprojects]

• decide whether to include those PNG images in the repository or to host them from somewhere else

I would also consider rendering to an SVG. Regarding storage I think the repository will be the best place for that since this ensures the images are present while external storage options might go offline at some point (if neglected).