Adding syntax highlighting to the code blocks in the README.md file

"Github flavoured markdown" (see [here](https://help.github.com/articles/github-flavored-markdown#fenced-code-blocks) and [here](https://help.github.com/articles/github-flavored-markdown#syntax-highlighting)) allow code blocks to have syntax highlighting. This is done by converting the 4-space-indent style code blocks to 'fenced' code blocks, attaching a language identifier to the block.

I've converted the code blocks in the readme to the fenced style (including removing the no-longer-required indentation of the code) and added the `sh` and `ruby` language identifiers to the relevant blocks.

You can see what it will look like [in my fork](https://github.com/natritmeyer/headless/blob/readme_tweaks/README.md) (should you chose to merge this pull request!)

I hope this helps :)