Use fenced code blocks for syntax highlighting

You were using indentation to mark code blocks. You need to actually use [fenced code blocks](https://help.github.com/articles/github-flavored-markdown/#fenced-code-blocks) to get the syntax highlighting, and [it's also good to specify `java`](https://help.github.com/articles/github-flavored-markdown/#syntax-highlighting) after the triple-backtick because it specifies the proper language to syntax highlight for instead of it making an educated guess.