Add gem install for markdown parser to README

[DanRathbun]

Documentation Issue

Add gem install for markdown parser to README file.

I spent a week dealing with weirdness especially with regard to links in extra pages files. It turned out that it all was caused by the default Rdoc parser being used for markdown parsing.

Neither the YARD documentation nor this templates README tells new users that they need to install one of the better markdown parsing gems. I assumed that they came with YARD or were part of a template. (Wrong!)

So it took Loran Segal (author of YARD) to track down the root of my problems and he told me it was me not having installed a better markdown parsing gem. (It seems this is one of those everyone familiar with non-embedded Ruby and Rubygems knows, so does not mention.)

I quickly installed Red Carpet and bing! all the problems disappeared.

And the doc generation seems twice as fast (or faster.)

So please do not let new users of the yard-sketchup plugin befall the same fate.

[thomthom]

Yea, there's a number of these hidden knowledges when one start to poke into YARD.

Btw, SU's docs uses RDoc, except for the .md files that accompany the class/module docs. I really wish we had Markdown across the board, but it's a non-trivial task to reformat all the documentation.

[DanRathbun]

Yes it's the extra files that I was having issues with. I'm working on "proofs of concepts".