GitHub has some cool additional markdown functionality called GitHub Flavored Markdown. When inserting code blocks in GitHub pages, messages, issues, or comments, I recommend using "fenced code blocks" instead of indentation. This makes editing and copy-pasting easier and you can use syntax highlighting in various programming languanges!
This is how you create a syntax-highlighted PHP fenced (```) code block (also works on coderwall, but currently not in the preview):
class ExampleDiFactory extends DiFactory
On GitHub, it will display like this: