Improve documentation for introspect

[tbenst]

Introspec seems really neat, but the current documentation isn't sufficient to understand the "why" of the tool, or how/when it is useful. Perhaps a few sentences explaining the "decoder ring" would help? Right now, I can understand the syntax, which seems to show how to draw the output of introspect, but that doesn't exactly explain the purpose / utility.

It also introduces a nifty table struct, which doesn't have any documentation--I'll open a new issue for that

[Mattriks]

To me it looks like that introspect was included purely for teaching purposes, rather than as a real development tool.