Update readme: bundle install instructions, kramdown not maruku, links to Mou

Updated instructions for bundler. Clarified how to install ruby. Clarified how to run jekyll in the bundle, and how watching the filesystem works. Link to kramdown, since the site uses that, not maruku. Fix links to Mou. 
And yes -- even a little tiny change to one file is taking several minutes to process on my 2.3 GHz i7 retina macbook pro. Kind of a drag.