Developer instructions for h-card and rel-me inclusion into themes

Based on conversations here: https://chat.indieweb.org/wordpress/2017-12-04#t1512409227038500 (and cross reference https://chat.indieweb.org/wordpress/2017-12-04#t1512409462787400)

We should better document and include an example for how to include the h-card output into a theme. Ideally it could be done to the level that a Gen2 person could reasonably follow to add it, perhaps by cutting and pasting a code segment.

There's apparently similar code for for rel-me, so that should be documented too.

Start with the two linked chat discussions, then inspect the existing h-card and rel-me output code and any theme-facing entry points. Document copy-and-paste examples for adding both outputs to a theme; done means a Gen2 user can follow the instructions without further guidance.

Written by the indexing model from the issue text.