Adding including external documentation from original appledoc website

Adding another document referenced in tomaz/appledoc#399

Converted HTML (as best I could) to Markdown.  Required using `<pre>` in a few of the code blocks because parts were bolded.  Also, added a header in one place so I could use intra-document linking.  And finally, made use of a newly added [GitHub feature](https://github.com/blog/1395-relative-links-in-markup-files) to include a relative link to the existing markdown document on comment formatting.

I'm not entirely sure that everything is still up to date in this document, but it seemed right to me, as I just used the contents to include some custom documentation.  This project rocks! :-)