As of maruku
engine (the default), writing table like
surround text, etc.
| Tables | Are | Cool |
| ------------- |:-------------
For this question, it seems the important extension here is "tables".
However if you want more Github flavored markdown, there are a few more listed at http://sholsinger.com/2014/03/jekyll-github-flavored-markdown.
Combining with neizod's answer I ended up using.
markdown: redcarpet
redcarpet:
extensions: ["no_intra_emphasis", "fenced_code_blocks", "autolink", "tables", "strikethrough", "superscript", "with_toc_data"]